To replace everything. Mail, calendar, drive, vpn, password manager, documents etc. What are the pros and cons relative to proton? What are the mobile apps like? What assurances do you have they won’t go full proton in the future? And other questions
Honestly you could easily selfhost all of that except mail and maybe a VPN.
Baikal for calendar. Vaultwarden for passwords.
I can vouch for Vaultwarden and Baikal. Two great essential programs I use.