A year ago I received my OnePlus 3T that was sent for a repair. The process erased all memory, so I wrongly decided that it was a good time investment to install Lineage OS without Gapps.
The imminent thing was to find a Play Store replacement, and F-Droid did the job. F-Droid is a great repository of open source apps. The downside is that lots of ‘normal’ apps aren’t there. I had to download Whatsapp and Signal from their respective websites for instance. Later I found Aurora Store, which connects with an anonymous account to Play Store and lets you download almost every app there. I couldn’t find my bank app for example, which was a bummer. Also, a lot of apps rely on Google Services to operate so a great deal of them just crashed or ran very slowly.
For the normal apps like clock, calendar and the like there are a lot of packs you can download and flash from recovery mode or install from F-Droid. Here is a list of must-use apps:
I first started with Lineage OS 16 and later moved to Lineage OS 17.1 nightly. I found that Lineage 16 worked fine while Lineage 17.1 had some compatibility problems with some apps, causing crashes when opening them, or not letting F-Droid install or update its apps.
Although usable, the experience is far for complete. There are a lot of things that do not work. In order to have notifications, you have to download and setup a service since the notifications come from Google (so Google can read every notification content, spooky). This service does not always work correctly and to see the notifications you have to enter the application, which makes notifications pretty useless. Localization does not always work and the phone needs a reboot from time to time because with apps like Telegram becomes unbearably slow. Maybe this is a problem related to Lineage OS only and other custom ROMs work just fine, but I haven’t researched nor tested other alternatives.
Despite all of this efforts, since the phone itself is closed source you can never be sure it disables telemetry completely, there may even be a dedicated chip inside for this task. The best option would be to not use a phone at all, which is the approach I would like to follow but my current way of life doesn’t permit it.
In summary, if you are concerned about the security of your smartphone I suggest you buy a Google Pixel and install GrapheneOS on it, but again having no smart phone is the way to go.