A cautionary note on Proton.
I've just spent a couple of weeks using a paid account with them for an important bit of business. (All very legal, but really important to me -> threat level -> secure provider).
There is no Linux client with a gpg signature. Last I looked, there is one with a sha sum. This is f(&!*&ing outrageous for a service that prides itself on privacy protection. I have complained and they say they've put it to their technical team to deal with it. Yeah, right...
You have to use webapps - sometimes they crash on my Firefox (privacy-respecting-ish browser), even if I have whitelisted/disabled extensions. Most times it works, sometimes it doesn't (like when you REALLY REALLY need it).
I use Claws for a local email client, which lets you make folders but filter rules have to be done in the web. I can't get Claws to search messages, so that's done on webapp as well.
There is no 3rd party client for Proton calendar, use the webapp, but you can subscribe to your calendar on other platforms as Read-only.
There is no other option on Linux for Drive - its webapp or nothing.
Honestly, I have no idea how much I can trust a browser, especially one with Firefox extensions. Maybe I should have made a different Firefox profile to handle this. Gets clunky.
The Android clients (Drive, Calendar and Email) work well on GOS, but the Drive client unchangeably default-opens to your Photos, that it insists on uploading. I didn't buy this to curate my social media posts, I want to go to my business folder.
Generally, I find the different approaches to file paths between Android and Linux to be confusing, and Drive hasn't helped. I've taken to the old-school strategy of emailing myself important documents just so I can rapidly find them on-site. That's a sign of failure, right there.
I have turned to my Mega cloud storage more often that I'd hoped.
Generally, there are quite a few bugs and undocumented bits and pieces that have had me tearing my hair out. Help is mediocre, usually wanting you to screenshot/video the problem. More frigging around...
I needed the Proton suite to just work and it hasn't. It really feels like its in beta - on Linux, it literally is. Its added a significant layer of extra stress to business that is already stressful.
Had I known, I wouldn't have bought. Maybe Windows and Mac experiences are different.
I might have gone with a Posteo email account, syncing calendar and task with Dav5x, and maybe Mega. It suits my threat model (I'm happy to be transparent to govt) and I know they work reliably.