I've got a lot of experience in that domain, since I've upgraded/installed by helping 7-8 friends & family to switch to linux in the last year here in Greece.
So the two most important things here is the speed of the CPU, and the amount of RAM. With 4 GB RAM on both laptops, means you need to aim for XFCe or Cinnamon, not gnome/kde, and not generally heavy distros like ubuntu/fedora. Also, you need to instruct them to not open a gazillion browser tabs, they will hit the swap (and eventually crashes) with 4 GB of ram.
The Acer laptop scores only 600 points on the Passmark CPU test, which means that it's only good for XFCE. So I'd suggest the Linux Mint XFCE edition.
The HP laptop has 1400 points, which are plenty to run Cinnamon (the default Linux Mint edition). For comparison, most new laptops sold today have over 12,000 cpu points, some go to 30,000.
Mint is the easiest to update, and install new software, and it will provide a familiar look to the user. I highly suggest though a few changes done by you before you give them back their laptops (if you're the one making the installation):
[Cinnamon HP laptop]
Install the Cinnamenu panel addon, to provide a more modern look to the main menu (and then modify it to look nice)
Install the dconf-editor and disable tap-n-drag. This default behavior can drive mad Windows users.
[XFce Acer laptop]
Modify the looks of the window manager to not have too many buttons, make it more windows-like.
Unfortunately, tap-n-drag is not possible to be disabled on XFce
[for both laptops]
Download Chrome. While Firefox is the preferred browser, Chrome is actually faster (particularly on youtube), and it consumes less RAM (tick its checkbox to consume less ram in the settings). This is seen as an anathema here, but the truth is, in lower end spec PCs, the speed difference between the two browsers is apparent.
Setup their youtube to play at 480p by default, and disable autoplay. Anything else will be very taxing to the cpu.
Install games from the repos for them, so they don't waste all their space with flatpaks later. Simple games like: sudo apt install aisleriot ltris gweled xye lbreakhouthd frozen-bubble gnome-mahjongg gnome-chess stockfish
Second keyboard language if they require it
Set up the power options to make sense
Create a webapp launcher for Photopea (using the chrome option, as it's twice faster on photopea than firefox), so they have a photoshop clone easily accessible (gimp won't cut it).
Set up the distro to be able to run appimages (test it with the new version of kdenlive for example from their website)
Install OnlyOffice appimage and set it up in the menus. Onlyoffice provides better msoffice file compatibility than libreoffice.
Install ublock origin or lite on the browsers, to avoid most ads and speed up the experience.
Proton is well developed for games, but not for apps. But Wine itself is not as well taken cared for. Without tricks, patches and prayers, most complex apps don't run on it. Or if they load, they crash quickly afterwards.
Which CAD app are you trying to run? If it's 2D, have you tried QCad/Cam?
You can install Haiku, the BeOS clone. That one runs well on less than 1 GB of RAM, and it had a new beta recently. Linux requires a minimum of 2 GB RAM these days to load 1 tab on a browser of a middle-complexity website, before it starts swapping. To really use Linux more comfortably, you'd need 4 GB, I'd say. And if you want to do 1080p video editing as well, then 8 GB. So, try Haiku.
It usually all works except the wifi in some models. The driver exists, and it's an available download in the official repos (just not in live cds, due to licensing), as long as you have a usb-to-ethernet adapter to install it. However, with Mint 22 I noticed that the wifi driver was finally included in the kernel and livecd by default.
I have the mid-2011 model, but that one has only 4 GB RAM. For 8 GB RAM you need to get to 2014 model or so. As long as it's Macbook Air with 8 GB RAM and 11.6 screen, you're in business.
Your best bet is an Intel Macbook Air with 11.6" screen from a few years ago. They're even lighter and smaller than the current macbook airs. I have one myself running Linux Mint 22. Just make sure it has 8 GB of RAM (it works with 4 GB too, but you can't have too many tabs open). They sell for $200 refurbished.
Linux mint will install and run from a usb drive as long as you unmount it upon loading its live version. Then it will allow to install on it during the installation procedure. I have an old Mac Mini and an old Macbook Air running Mint 22 that way.
If the PC you're building has the latest and greatest hardware in it, you might find that Linux might not support that stuff yet. You might get lucky, but you might not either. It usually takes a little while to get new hardware supported. So it might be a better idea to install Linux on your older computer, then there's no reason to buy a new PC anyway. Linux uses about half the RAM that Windows uses, for example, so it's like you did an upgrade anyway. As long as you have over 4 GB of RAM, you're fine for desktop usage. Windows requires 8 to run as well that Linux does at 4. You'd only need to upgrade if you're after extreme gaming support.
Depending which version of the MacPro you have exactly, that machine from 2010 is around the speed, or slightly faster, than a Raspberry Pi 5 with 8 GBs of RAM these days. The problem is the energy consumption, not really a green machine to run.
Raspberry Pis are also ARM-based, and you can use them as desktops. Only problems are that they aren't very powerful for media usage (e.g. video editing, 4k video decoding on youtube, blender etc). If you're not into such high performance media production, then sure, they're fine for everyday usage.
No, there is a third option: you freeze the API for the extensions. That way, nothing breaks. And if an app uses private APIs (or public APIs that are not meant for extensions' use), then and only then you treat it as unsupported.
And yes, the constant breaking is a big, big problem. I use 6 extensions to make the desktop the way I want it to. In every release, I get at least 4 of them breaking for several weeks each time. The last time, the dock extension I used broke with the new Gnome version, but when it got disabled, the "favorite" icons on its dock did not reflect on the Gnome's default dockbar. All that stuff, are unacceptable for a proper usage in 2024, especially for people coming from Windows that expect stability (no matter what people say, Windows IS stable). I use Linux since 1999, but it's that kind of stuff that i can't stand. I want stability. The days when I was hacking on Gentoo in 2003, are long gone. I'm now in my 50s and i don't have time for that shit.
I use Gnome, and I'm not a hater, but if you're expecting some harsh criticism for it, here it is: Extensions breaking so easily should not happen. It's an extreme pain in the butt every 6 months. They should establish an allowed API that's frozen, while extensions that use private api calls, don't get posted on the gnome website/extensions app, so they're harder to find. Simple.
I've got a lot of experience in that domain, since I've upgraded/installed by helping 7-8 friends & family to switch to linux in the last year here in Greece.
So the two most important things here is the speed of the CPU, and the amount of RAM. With 4 GB RAM on both laptops, means you need to aim for XFCe or Cinnamon, not gnome/kde, and not generally heavy distros like ubuntu/fedora. Also, you need to instruct them to not open a gazillion browser tabs, they will hit the swap (and eventually crashes) with 4 GB of ram.
The Acer laptop scores only 600 points on the Passmark CPU test, which means that it's only good for XFCE. So I'd suggest the Linux Mint XFCE edition.
The HP laptop has 1400 points, which are plenty to run Cinnamon (the default Linux Mint edition). For comparison, most new laptops sold today have over 12,000 cpu points, some go to 30,000.
Mint is the easiest to update, and install new software, and it will provide a familiar look to the user. I highly suggest though a few changes done by you before you give them back their laptops (if you're the one making the installation):
[Cinnamon HP laptop]
[XFce Acer laptop]
[for both laptops]