Safari stops loading webpages

I'm having this issue too, on an M1 Mac running macOS 12.3.1 and Safari 15.4

This is definitely something up with either Safari or macOS. When it happens I have the same symptoms as you, but all other network traffic continues to work fine (Discord, Slack, Messages, etc). No amount of quitting Safari and restarting will fix it until you just wait a few minutes and it starts working again. Does it every few hours or so.

Go step by step and test.

1. Force Quit Safari, launch Safari holding the Shift key down.

    How to force an app to quit on your Mac - Apple Support

    About pop-up ads and windows in Safari - Apple Support

2. Startup in Safe Mode. 

   Start up your Mac in safe mode - Apple Support.  

    Quote:

    It also does a basic check of your startup disk, similar to using First Aid in Disk Utility. 

    And it deletes some system caches, including font caches and 

    the kernel cache, which are automatically created again as needed.

3. Clear History

    https://support.apple.com/guide/safari/clear-your-browsing-history-sfri47acf5d6/mac

    Please read the article before clearing history, 

    this is like a low level resetting of Safari without affecting passwords and bookmarks.

4. If Safari doesn't open a webpage or isn’t working as expected

    If Safari on Mac doesn't open a webpage or isn’t working as expected - Apple Support

I’m having this issue with safari on all of my devices (2020 MacMini M1, 2015 17” MacBook Pro, 10.5 iPad Pro, and iPhone XS Max). When I run a speed test on each browser it is significantly slower than FireFox, Chrome, and On device apps. I have cleared the cache and it is still slow. I’ve switched to FireFox as my browser for now (it’s the fastest).