iMac (Sonoma 14.4) won't save default apps for video, .7z

My iMac (Sonoma 14.4) refuses to change default video app to VLC. Instead it reverts to Books as the default. When I click a video to open, Books is the default app but Quicktime opens the vid. Very weird!!

I make mp4s and most are on a portable hard drive. I thought this might be a problem, so I ensured VLC remained on the iMac hard drive, moved some videos to the Desktop, and tried to change the default to VLC, but same problem.

This also occurs with .7z files. I use Unarchiver, but again the iMac refuses to change the default app to Unarchiver, instead defaulting to Archive Utility.

I bought Power Suite to hopefully resolve the issue, but it doesn't.

Any suggestions? I have a feeling I may need to update Sonoma or get the latest OS update, but maybe one of you Mac lovers has a fix? Thanks in advance for your help.