I have been installing from the disk my 2010 office on different computers of mine for years.  Never had an issue with it on more than one computer. 

I did just buy MS Office last month from Stack Social for $30.  I see price went up to $40 and now they are out of stock.. They must have gotten access to a bunch of licenses to sell off when Microsoft needed to make a bunch of "sales" for their sales goals?. No mater how they got the software, I bought it, downloaded and got key codes for full install/activation - working just fine. 

Maybe they will get some more in future.

https://stacksocial.com/sales/microsoft-office-professional-plus-2021-for-windows