It seems you already did quite a lot of troubleshooting in an effort to isolate the cause, including all the suggestions in If Safari on Mac doesn't open a webpage or isn’t working as expected - Apple Support. Emphasis on all because there are quite a few of them, ranging from essentially useless (reload the page... really?) to potentially useful ones such as checking various Safari-specific settings, and using a Private Window. Those steps might isolate some potential causes and could suggest additional actions to take.
Add this potentially useful troubleshooting step: Start your Mac in the Recovery mode appropriate for your model MBP:
Use macOS Recovery on an Intel-based Mac - Apple Support
Use macOS Recovery on a Mac with Apple silicon - Apple Support
Once in Recovery, select Safari. Load a few web pages and determine if the same problems persist. They probably will not, but if they do, then the problem is likely to be external to the Mac. Really odd cases are often resolved by resetting the wireless router and / or modem.
If the problems do not persist in Recovery mode, then create a new, temporary User Account according to Add a user or group on Mac - Apple Support. You can skip all the personalization steps including using your Apple ID. Launch Safari in that Account and observe again.
You can delete that temporary Account when you are finished with it: Delete a user or group on Mac - Apple Support.
Please write back with your observations.
