You can always ask online community here or on other platforms since they can provide you with exactly what you want.

That would be no. Even if you use ADB to remove bunch of packages that make connections you still can’t be sure if you will have privacy since stock ROM is proprietary. DNS can block some connections but Android and apps can use their own DNS if they want so it also depends.

If question was about security then yes, sticking with stock ROM is usually more secure although many argue that GrapheneOS holds highest security standard. DNS can also improve security since it can block malicious domains, that depends which DNS provider you’re using.

I think it provides fake data but don’t take my word.

Data only needed for that specific service to function

Aurora Store is 3rd party client for Google Play Store while MicroG is open source implementation of Google libraries so they are not quite comparable.

I’d say MicroG with Aurora Store is most private you can be if you really need to use Google services. You can use Aurora Store with anonymous Google Account that they provide you and MicroG is only sharing necessary data with Google servers.

If I’m not mistaken Firefox’s tracker blocker on strict and uBlock Origin do the same job

Thanks but I don’t use web browser on mobile and probably if I would, I’d use IronFox or IceRaven

Well yes, anyone can compile its own version of Signal and use it and it will work as long as there aren’t some major changes to its communication protocol

I’ve also tried to use Mullvad as regular browser but even though I turn off always private mode, after restart all cookie exceptions disappear

Even though I don’t use chromium-based web browsers because of its monopoly, it would be nice if we could integrate brave shields into ungoogled chromium so people wouldn’t have to deal with all bloat and surprises from Brave

Mullvad and IVPN

You don’t need to give any data, not even email address