I had a run of luck finding two more possible issues. Here's hoping your patience has not run out, my helper.
If it works I'll make a major release.
Hello. The good news is that it finally works! The bad news is that it is still unplayable. After launching the game there is a white screen with two buttons (one with some weird string of letters). After pressing the left one, which is 'start' I assume, the screen turns black and there is nothing on it except the 'NO DC' message in the left upper corner.
Also, nvidia says 'reset to default settings from the Nvidia Control Panel.' https://www.reddit.com/r/runescape/comments/m6cv00/comment/gr50a9m/
Maybe there's light at the end of the tunnel.