This reminds me of the temperature of lights that my backyard neighbors have. Everyone is entitled to their own preferences when it comes to light bulb temperature... until they do it wrong.
Take a look at the models that Gadgetbridge supports. Your data stays on your phone. There are no servers to connect to. You should have roughly the same experience on any Android device.
As for tracking sport sessions, look at what each model offers. I use it to sync my PineTime and Mi Smart Band 7.
I really like using the features that Mi Smart Band 7 has to offer AND knowing my data stays on my phone instead of going to servers in China.
Caveat: Recent Amazfit/Mi devices have needed you to set up the device in their proprietary app first to generate a pairing key.
If you're looking at running LineageOS, have you considered just using your banks website? There may be some functionality lost, like push notifications, but you may be able to pivot to email or SMS notifications. Are there app only functions, like mobile deposit? Different banks do things differently.
Give ncdu a look. It is on Linux. It will allow you to see big chunks of data. I'm sure someone has a container version of it, but you can run it straight from the terminal.
I've got a D9 running with Valetudo! It's fantastic! Not only am I not worried about privacy concerns, but it works with my HA seamlessly. Check out their list of supported vacuums.
Oh for sure! Droid-ify offers a few different installation methods. The Legacy and Session install options are what you are used to. With those methods, you are prompted to download and install with each update.
With the Root install method, updates can be downloaded and installed in the background using root privileges. Lastly, and I think most intriguing, is using Shizuku. Shizuku is a utility that will give you close to root access using ADB. See link for details. So, with the Shizuku install methods, Droid-ify can keep all your F-Droid apps up to date with little intervention from the user.
Footnote: Because Shizuku leverages ADB, it needs to be started manually after each reboot.
On Android, we're used the "Play Store" being both the app that facilitates downloads as well as the collection of apps available. With F-Droid, you can add additional collections of apps to make available for download.
You might add an additional repository to gain access to apps not in the main F-Droid repository. You might add a developer's repository to gain access to updates to their apps before those updates hit the main F-Droid repository.
Divest is the developer repository for app maintained by Divest OS, a fork of Lineage OS.
There is safety there, but you're just as safe using the the developer's own repository for their apps, like NewPipe, Collabora, or the Guardian Project.
Fun fact, according to tradition, St. Nicholas punched a rival cleric at the First Council of Nicea in 325.