After installing a licensed copy of PowerDVD 21 on Windows 11, the software would not start.

If I double-clicked a video file (after assigning the Default Program for that file type to PowerDVD), the file would play, but there was no control, except to press Alt-F4 to stop the playback.

SOLVED:
I solved this issue with the following steps:

1. Right-Click on the PowerDVD 21 shortcut on the desktop. A context menu appears.


2. Choose "Open file location". A File Explorer window appears, with "PDVDLP" selected.


3. lick on the file type in the header to sort by file type.


4. Perform the following steps for EACH file of type: "Application".


5. Right-Click on the Application type file. A context menu appears.


6. Choose "Properties". A properties dialog appears.


7. Click on the "Compatibility" tab. Compatibility options appear in the properties dialog.


8. Click on "Change settings for all users". A new dialog appears.


9. Click to check-mark the check-box called "Run this program as an administrator".


10. Click "OK" on the new dialog box. The new dialog box disappears.


11. Click "OK" on the remaining properties dialog box. The remaining properties dialog box disappears.

PowerDVD 21 should now run as expected on Windows 11.