You have the non-snap, non-flatpak package (aka deb package) of Opera version 110.0.5130.39 and the libffmpeg.so from the zip file at https://github.com/Ld-Hagen/fix-opera-linux-ffmpeg-widevine/releases/tag/nwjs-ffmpeg-0.87.0 in "/usr/lib/x86_64-linux-gnu/opera/lib_extra/"?
Make sure hardware acceleration is on at the URL opera://settings/system.
Goto the URL opera://gpu. Does it show that most things are hardware-accelerated? If not, on Linux, you might have to mess with some flags at the URL opera://flags and or some command-line switches (see https://www.reddit.com/r/archlinux/comments/x1z0a0/comment/imj7zmu/ and https://new.reddit.com/r/linux_gaming/comments/11gak0r/gpu_accelerated_video_decoding_vaapi_in_chrome_or/ for example) to get things hardware-accelerated.
When you launch Opera from a terminal, does it give any errors when trying to play shorts and reels?
After trying to play one of the shorts and reels, you can goto the URL opera://media-internals and click on the box for that player to expand it and see what errors there are. You can also look through the whole log.
You can test if it's a browser-detection issue and pretend to be Chrome. See https://new.reddit.com/r/operabrowser/wiki/opera/known_issues/#wiki_can.27t_log_in_to_twitch for example of how to do that.
I see the error often means you have an unstable connection, but I'm going to assume that's not the case.