Greasy Fork is available in English.
Scan page for Youtube embeds and urls and replace with Invidious.
< Rückmeldungen aufYoutube to Invidious
Yes, turning dash off is the only thing I can recommend for you. It should not have any effect on thumbnails. Unfortunately I cannot do any testing for Safari.
Redirect embedded video to hd720
I encounter an issue with embedded videos in Safari MacOS. Safari doesn't support DASH, but embedded videos get redirected to DASH and so I can only view +/- 10 seconds of the video.
Okay, I have found the beta feature in the code (also before posting the issue), but it seems not as snappy as having the dash on. The thumbnail and buttons take longer to load.