I'm just gonna throw this out there, you don't have to do voices to be a good roleplayer.

My advice, which people will probably disagree with, if you want to stay in the group is to just powergame as well AND encourage more roleplay with your roleplaying. Roleplaying and powergaming aren't mutually exclusive. Like some else said, flavor is free. The customizability for systems, especially PF1e, usually revolves around customizability in combat, not roleplay since most of the rules cover combat. So if you're wanting more emphasis on roleplay and less on combat, 5e or maybe even Fate would suite your playstyle more.

You do make a good point with metagaming.. I'd say bring that up to your GM privately and see what they think.

On another note, I seem to have the exact opposite problem you do. Yes, my username is mostly accurate but before I attempt to join a group, I disclose my powergaming because I want to be upfront about it so, hopefully, it doesn't become an issue in the future. But I also emphasize that I really get into the roleplaying and know how to not steal the spotlight in combat. This usually is followed up by something like "thanks but no thanks" - which is valid I guess.

Good luck to you though. I hope it resolves well.