I have my own domain, so offboarding from Proton was pretty easy, just exported all my mail and then setup the new mail provider with my email and imported them all.

There are a number of email providers I looked at when switching. Ended up going with mailbox as I was more confident about privacy of a company in Germany than Australia and they were a bit cheaper. Posteo seems like a good option if you don't have your own domain. I also looked at Tuta, but their lack of import killed them as an option, I'm not signing up for a higher subscription level to get that feature.