Install Video DownloadHelper for Firefox. Open whatever you want to watch and copy it’s url from Video DownloadHelper. Now, either open that url in mpv (might require yt-dlp) or download it (I’d also recommend yt-dlp for this, since DownloadHelper sometimes embeds watermarks) and watch wherever
I guess you’re using Nvidia if you’re having problems with Wayland? Maybe try running nvidia-settings as root, adjust your desktop resolution, refresh rate and settings there. Than save it to /etc/X11/xorg.conf.d/20-nvidia.conf