Do an authoritative restore of the SYSVOL on your old DC. I have often seen single DCs that get their SYSVOL DFSR metadata stuck and no one realizes, because it doesn’t need to replicate anyway. You might have a really old DFSR even saying it stopped replicating, but it’s likely disappeared since.
Another thing… I don’t recommend Windows Server 2025 for a DC. It’s got too many bugs and issues.
