RE: Why must port 445 be opened in SQL during installation or rollup upgrades
Hi,
As you said, 445 is used for SMB and for D365 installation Microsoft uses it to copy template database file on SQL Server using a UNC path.
An extract from docs:
"Active Directory service required for Active Directory access and authentication. This is used by Server Message Block (SMB) during organization creation to create a 'template database' from the installation location on the Dynamics 365 Server to a UNC path on the SQL server."
I hope this answers your question.
Best,
Wahaj
(if it helps, mark it verified)