What's the current level of proton mail accessibility across macOS and iOS please?

Hi everyone, hope you're doing well and staying safe. Even though I'm posting this question in the Mac area of the forum it pertains to both Mac and iOS.

Please can anybody explain to me, what the current level of accessibility of proton mail is across Mac and iOS? Are there any got use or things to be aware of what's the best way of accessing proton mail please? Thanks very much for your help everyone :-)