RE: Dynamics GP 2018R2 Compatibility with SQL Server 2019 and Windows 2019
Like Tim said, this can cause issues more than just whether or not the databases can be restored and logged in to. Chances are, the databases would restore fine and you could log into GP.
However, GP Utilities performs hard version checks against the version of SQL, so if the version of GP that you're on doesn't have that version of GP hard coded as supported, then Utilities won't run and you won't be able to update without a SQL Downgrade of your databases, which is essentially scripting out every object, recreating all objects and databases on the old version of SQL, then DTSing all the data into it.