The best way to install them is through the F-Droid store, which is a catalogue of FOSS software for Android. It’s installable by downloading the .apk file linked on the front page of the F-Droid projec’ts website. The mentioned apps from the Karlsruhe Institute of Technology can then be found by searching for “SECUSO”, which is the name of the research project behind them all.
Alternatively, you can also get them through the Google Play Store under this link or again by searching for “SECUSO”.
In particular, I recommend getting the QR code reader, because many of the free-to-use scanners route everything you scan through their servers, so they’re obviously collecting your data.
I’ve been on lineage for ages and recently tried out /e/, was pleasantly surprised. Reminded me of a reskinned lineage with some FOSS/F-droid apps integrated into the system and some extra privacy stuff.
I particularly like the fake location and app tracker features.
When it comes to standardisation, there’s a minimum defaults-based system called GSI where the same distribution works across a lot of devices. But minimum defaults leaves a lot of devices specific features dead in the water. It’s more for development than distribution.