Edit: TL/DR I think that @JeroenH gave a better explanation!
Hi @mgfp and @gcrl,
Please excuse me as well if I’ve misunderstood the question. Also, I realise I’ve probably come across as a bit of a “know-it-all”. When I think I know something that may be of interest to others I tend to say it and sometimes this can come across as arrogant, so please excuse me if that’s the case. Even if I think I know something I’m very happy to learn that I’m wrong and have someone correct me, so if that’s the case with anything I’ve written in this thread then please explain it to me!
About FP Open OS, LineageOS, /e/, Shift OS-L etc. Apart from /e/ these are all pretty similar, as far as I can tell. I didn’t manage to find much info on Shift OS-L and others here are much more knowledgeable about FP Open OS so I hope someone will correct me if I get my facts wrong here.
FP Open OS and Shift OS-L are similar, they are both Android without the Google Apps or Google Play Services (GPS). Unfortunately many apps require Google Play Services, so without this these OSes have reduced functionality vs normal Google Android unless GPS or an alternative is installed.
LineageOS is also a flavour of Android without the Google Apps, but it has been customised a lot and offers lots of configuration possibilities. It still needs GPS or an alternative to be full featured.
With all three of the above the Google Play Services and Google Apps can be installed afterwards. Or an alternative, one of which is MicroG which aims to replace all of the services from GPS with open-source versions which don’t communicate at all with Google.
/e/ is based on LineageOS plus MicroG, so it has just as much functionality as normal Google Android but without the GPS communication with Google and with the added configuration possibilities of LineageOS.
Since MicroG can be added to LineageOS, FP Open OS and Shift OS-L (as far as I know) you might think that /e/ is still not significantly different. However, the /e/ team have also removed as much other communication with Google which is inside the rest of Android as they can. There are still some things to fix, but there is still much less communication with Google than any of the other options above.
They also provide their own app store and their own privacy-respecting cloud services (drive, mail, calendar, contacts, notes, tasks and search engine). In this way they replace all the other Google things which people normally depend on as well, which to date has probably been the main reason that people have almost always failed to go completely Google free.
There is a “product description” on the /e/ wiki here that gives more details: https://gitlab.e.foundation/e/wiki/en/wikis/e-product-description-pro-privacy-Android-ROM-and-online-services
If anything’s wrong or not clear please tell me.