I honestly can't tell if this is sarcasm

It's not sarcasm. Device A creates a private and public key on device and sends public key to device B. What's the problem here?

I'm guessing you mean "tapping" the devices together or sharing keys through a webcam or a handwritten note. Yeah that is a pain.

Okay fair enough, Signal's end-to-end encryption is a lot more complex than that but really how is it a terrible end user experience?

It's not terrible. It's just worse in some areas. Which is of course a worthwhile trade-off for many people. Just... Some people don't really care about the privacy part

Signal isn't nice to use on multiple devices. I'd lose my chats if I lost my phone without backing up the keys. Actually WhatsApp somehow deleted my chats even though I restored my phone from backup, idk. Signal also stops notifying you if it goes out of date.

It's fine for the use case they're meant for. Unlike Instagram, they had these usability limitations from the start, and they delegated auth completely to the phone providers.

On Facebook, I cannot receive messages. It only shows me a bit saying it's encrypted.

I used to help a nonprofit with their facebook account, made it a real pain in the ass for everyone involved.

Of course facebook has no customer service and their slop docs were of no use.