Can't open Safari

Does this issue also happen when starting in Safe Mode ? Restart computer and immediately hold the SHIFT key until the Apple Logo appears and release. It does a repair Disk, clears cache files and only loads Apple Software, extensions and Fonts. It will take longer to load - Normal. Once logged in - Test and report back please.

I see you referred to the Big Sur upgrade link. Safari is antiquated browser. If you need to install Big Sur go directly to the App Store, after following the tip:

https://discussions.apple.com/docs/DOC-250003076

If you are trying to use Java, other browsers are more current, as this tip explains:

https://discussions.apple.com/docs/DOC-250003586

I have two comments. First, it would be helpful to know exactly what message(s) you are getting. Second, do you mean that Safari can't open certain web sites? Safari is not used to open other apps.