Frostbite engine and F1 23

You're not going to get any official response to a question like this. Even getting official confirmation that there will be an F1 23 game is pushing it.

My complete guess is that we won't see a new game engine until support for last gen. consoles is dropped, and when it does it will be a new version of Codemaster's EGO engine.

Visually UE5 is looking really interesting/promising but I have absolutely no idea how suitable it may be for racing games. Frostbite is not exactly cutting edge at this point, is it?

What makes you think that Frostbite would be a good candidate? Genuine question, no rhetorical artifice here.

ACC was made on UE4, but Kunos has stated already that they'll be moving back to a proprietary game engine for AC2 for better flexibility and specialized tools. All Project Cars titles were made on SMS' proprietary Madness engine too – and Codemasters probably acquired it along with the studio not a while ago.

UE5 looks amazing, indeed. But I can't say what a hypothetical new iteration of the Ego game engine would bring to the table, and most definitely can't say what Frostbite could offer over it – hence my very first line in this post 🙃

Not long ago we also had that Anthem obituary by Jason Schreier back when he still worked at Kotaku. It's a long piece, but you can zoom in to the parts he mentions Frostbite and the problematic development and in-house support.

Codemasters confirmed that they were making a new WRC game which would be yearly editions starting from 2023. It's meant to be using the Unreal engine so potentially any F1 games could follow suit. It could be in a new Ego engine, who knows?