@Greg Rewis can you please further clarify the Sharing button that came with Spring 21?

I saw the idea (https://trailblazer.salesforce.com/ideaView?id=0873A000000LmluQAC) was closed with reference to Spring 21 release (https://help.salesforce.com/articleView?id=release-notes.rn_forcecom_manual_sharing_lex.htm&type=5&release=230) but according to the document from Salesforce (https://help.salesforce.com/articleView?id=sf.granting_access_to_records_lex.htm&type=5) the button was not built for all objects.  Example what about Campaigns?

Also I see the Sharing button is now on the page layouts on the back-end but I am not seeing the button when actually looking at records.  I am the system admin.  Is there something I am missing that requires configuration?