Is it a problem with Safari 26 or is it a problem on Facebook's side?
I had similar issues like the OP or it would show 1-4 feeds and give an error message on Safari 26 and Sequoia.
Now that I have upgraded to Tahoe I get a different issue on Facebook. I get an error occasionally where videos won't show/play on Facebook and the only fix I have found is to force quit Safari and reopen it.
So far the only issues have been on Facebook, all other websites work fine.