There is nothing wrong with FastMail, I just don’t like that they are based in Aus and are under the Five Eyes situation. I say this as an Australian who lives in a different country. I would prefer privacy locked, but from their transparency reports, they do seem pretty secure.

I’m not opposed to it being calendar only, but if it has email also then that is a bonus

Thanks for the links. I’ve heard of Librewolf but never tried it. Will give it a spin.