This is specifically about KDE’s own Linux distro, which is still in alpha.

Oh, looks like you’re right. Thanks for the correction.

Go piecemeal. Proton is a good deal if you actually use all their services, otherwise it’s overpriced.

For mail, mailbox.org, posteo.de, and fastmail.net seem to have good reputations. They’ll all allow you to bring your own domain (edit: not Posteo, my mistake), which I highly recommend so that it’ll be easy to switch providers again when whichever one you choose turns to shit (yes, I say when, not if, because I am just that jaded at this point).

For passwords, there are a lot of choices, but the most future-proof is probably to keep a local Keepass DB and sync it across devices any damn way you want. Bitwarden used to be good but I don’t know anymore. They’ve backed away from open source a bit recently, and I can’t even tell at a glance what their free plan offers anymore. Maybe look at https://vaultwarden.com/ instead.

For VPN and storage…I dunno. There are a lot, and most of them seem kind of shady tbh. I’d be interested in hearing others’ advice on this since I’m not sure what’s good these days.

Edit: I’d REALLY like to hear recommendations for Docs and especially Sheets. Everything else I’ve used is a UX nightmare, particularly on mobile.

I can’t say if it’s difficult to revert because I’ve never wanted to

Same.

If you never do anything advanced, it’s as easy as any stock UI.

If you do want to do advanced things, it’s probably your only option because most stock firmware is ass on consumer-grade devices.

Most things should work just fine. There’s not all that much that requires x86.

So the real question is, what does your mom need/want? NextCloud? Jellyfin media server? Ente photos?

Maybe just a media center? Basically an Apple TV on crack?