Hey... If you want to add an video to a thread mostly you have to upload it to an album first.
Notice the max. video/image size (4096px x 4096px) otherwise it will abort.
If you have it already in an album you can copy the video/image address and finally link it in a thread. I think images are mostly direct postable but videos need to be linked...
Yeah I know it's not that simple like insta 😅 but it works...