Nextcloud also advertises an office suite, though I haven't tried it. Nextcloud also apparently integrates with OnlyOffice, though I haven't tried that either— Apparently Nextcloud's own office suite is a rebranding of LibreOffice.
I'd probably go with OnlyOffice, either on its own or integrated into Nextcloud.
Have been a customer for years, great service run by humans.
Everyone in my immediate family has 1 or more email addresses in our family domain, and I have a couple of fun/project domains their too, for $0.00 above what I was already paying for iCloud.
Zoho is an alternative, can do custom domains, website hosting, email, productivity suite.
If you have any issues, a real person will answer your support ticket.
You can have up to 3 domains configured per family.
And I really really don't like iCloud's file system.
Protonmail ? If its email you're after you can point your MX at them.
What are my alternatives besides Office365?