If you implement an allowlisting proxy, the number of required domains for M365 / Azure is something like 120 [1]. Google basically requires three, tunnel.cloudproxy.app, *.google.com and *.googleapis.com. Amazon requires *.aws.amazon.com, *.amazonaws.com, *.awsstatic.com, *.api.aws and *.aws.dev.
Microsoft has some great domain planning.
[1] https://learn.microsoft.com/en-us/microsoft-365/enterprise/u...