For mobile, I use QuillPad as my keep replacement
Proton
Empowering you to choose a better internet where privacy is the default. Protect yourself online with Proton Mail, Proton VPN, Proton Calendar, Proton Drive. Proton Pass and SimpleLogin.
Proton Mail is the world's largest secure email provider. Swiss, end-to-end encrypted, private, and free.
Proton VPN is the world’s only open-source, publicly audited, unlimited and free VPN. Swiss-based, no-ads, and no-logs.
Proton Calendar is the world's first end-to-end encrypted calendar that allows you to keep your life private.
Proton Drive is a free end-to-end encrypted cloud storage that allows you to securely backup and share your files. It's open source, publicly audited, and Swiss-based.
Proton Pass Proton Pass is a free and open-source password manager which brings a higher level of security with rigorous end-to-end encryption of all data (including usernames, URLs, notes, and more) and email alias support.
SimpleLogin lets you send and receive emails anonymously via easily-generated unique email aliases.
For sheets, there's OnlyOffice or Collabora
For keep, there are a lot of options. NotallyX allows you to use an external storage folder, but you would need to figure out how to sync it (Syncthing should work if you set it up correctly)
Joplin, Obsidian, and Standard Notes are popular recommendations, and if you are self hosting there are some other excellent ones.
However, you might consider a notes/memo webapp like tinylist, which is great and easy to use if not as fully featured as some alternatives.
For what it's worth, Proton owns Standard Notes. I think they largely used the acquisition to make Proton Docs and there is no perk like free or additional access to Standard Notes than any non-Proton user has.
I use Obsidian which syncs to my home server.
Only office could be one solution for the sheets.
Dark Notes is hand down the best Keep alternative.
https://play.google.com/store/apps/details?id=com.akapps.dailynote
It has local backups but you can sync them with Syncthing or similar.
There’s Collabora Office for sheets.