UAC dialog opens for every single PDF in the same session.

On a Win 10 Home PC, I have Adobe Acrobat installed and all updates done. Adobe is set as default app. Several days ago, the following problem started. Whenever I try to open a PDF using Acrobat, the User Account Control dialog opens. The UAC opens EACH time for every single PDF in the same session. I open 50 to 100 PDFs in any one session.  

On a different PC with Win 11 Pro, the PDF just opens with Adobe, no issue whatever, although the settings in Adobe ( and in Edge and in Chrome) are exactly identical.

 I’d be very thankful for a solution. This issue is driving me batty. (PS: Would updating to Win 11 solve this? If yes, I would upgrade instantly). Many thanks!