Installing the PTR does create the “Diablo II Resurrected (PTR)” folder in c:\users\username\saved games\ as it should.
However, the actual PTR client (bnet version on Win11) then completely ignores that folder in single player/offline mode and instead pulls from (and writes back to) “Diablo II Resurrected”, resulting in live client saves being subject to whatever intentional breaking is required to properly test things on the PTR.