An update: It only breaks on non-mobile devices, e.g., a desktop PC, or iPad. If you try your URL example on an iPhone, it will present you with the option to share with a group. Apparently, it's because m.facebook.com manages the Share Dialog differently. That is to say, PCs and tablets now handle it differently than iPhones, but they didn't before. Some time before March 7 2024, Facebook broke it - either inadvertently, or intentionally. If someone from Facebook ever looked at these posts, perhaps we could get an answer why.

What's even worse is that the new share_channel seems to not work with all url encoded characters. A comma seperated list for example is not working correctly. It keeps the encoded value instead of replacing it with a comma.

Currently it doesnt work at all on desktop. All the share dialogs redirect to https://www.facebook.com/share_channel/ which says "Page isnt avaiable"

It is not possible to share anything currently