I’m just some rando with no expertise to speak of … but … I just installed Vivaldi on Android and went to
https://coveryourtracks.eff.org/ and https://amiunique.org/fingerprint.

After testing Vivaldi, they both say it has a unique fingerprint.

Do these sites really tell the fingerprint story or is there more to it?

Best tip i can give you is this…

https://discuss.grapheneos.org/

Make an account there and find all your answers. The community is VERY knowledgeable. Good luck

Yes. You can go back to stock.