No. The main diference is that you write a software for Android, it doesn't work in gnu/Linux (without extra layers), but if you write a software for steamOS, literally you are writing a software for gnu/Linux. SteamOS is an arch Linux modified to be immutable with a custom (and free) kernel with extra support that they merge after in mainline, with the steam app oppened by default.
SteamOS use all the software stack for gnu Linux. Android develop their own stack and work different.
But you want to use systemd-boot? Obviously you need to install systems-utils if you want to install systemd-boot, but you can use grub or something else bootloader
You can install gentoo-kernel-bin and everything works fine.
About SystemD, you needn't systemd as init, but you need systemd as udev or other things. Only follow the guide with a non-systemd profile
Nowadays a lot of hardware works very well on Linux, the main approach of this vendors is not the compatibility (has guaranteed but as you say in a thinkpad you have the same compatibility), the approach is about a free software (or mostly free) firmware, and in this case, free and secure implementation for the firmware an all secureboor chain
If snap or flathub repos are in the store, any mainstream application be in.
In the other side, if you don't know what are you doing and install random packages, the most probably is that you'll broke your system
The normal people doesn't install software external to the store or configure the system a lot, in IOS you can't do this things and everyone is fine.
For share network in gnome you can do it with a button in the WiFi settings
In my firs time with linux I install ubuntu (maybe 12.04, I dont't remember, it was gnome 2) in the only PC in my parents home, I delete windows, and we was using it 2 years without knowing what is a terminal and everything went fine, the problems appeard when I was discover the terminal hahahaha
In my opinion the hardest thing in linux is leave to use propietary or exclusive software for windows, the first think you must do is leave to use propietary software in windows, and when you can live without windows exclusive programs, switch to linux.
You can start for ubuntu or other linux friendly distribution, doesn't care, afther the migration you can try other for curiosity without risk
Gentoo have both sides, the cool community and the suckless community xD You can check it in the telegram groups about gentoo