As one of the good QB tech support agents, I apologize on behalf of my inadequate colleague. Intuit doesn't stop supporting QB '21 until May '23. The timing of this encounter makes me think this was either someone who was still in training or fresh out and was uninformed or misinformed. Intuit stopped supporting QB '20 after May 31, 2022. Your issue seems like it's outside of QB, honestly. .NET framework or MSXML are possibly to blame...or MS registry.
