Already done: replaced SendGrid with Sweego.
Later: move domains from US registrar to EU based.
The difficult bit is the Microsoft Office because we are also using Azure DevOps for code, tickets, wiki and ci/cd.
Just moved all my hosting and dbs from a US company to Hertzner after 15 years of good service. Moving domains now.
Unfortunately there's not that many and often the process is broken.
You are talking about DNS zone hosting which can be separate. And I always prefer to keep it that way.
Sometimes hosting companies suspend accounts. If that happens, it's useful to have your domains and backups with different providers.
Context: I used to run a domain-related service that used registrar api's and gandi's seemed the most well thought out by a considerable way. The drawback was they're quite expensive for registrations/renewals unless you're doing it at volume.
I had reservations about them being a French company wrt support but their API was so good I never needed to contact them on anything.
Definitely worth a look.
It's all in there.