Thanks for the user test :) I updated the game loop to be separate from the rendering loop. Any chance you can tell me if it is still slow?
Just tried it on my son's machine, which is the same hardware as mine (but running Windows rather than Linux, both of us using Brave for browsing) and it's fast there too. On my machine, even the clock rendering is dramatically slower than real-time; I'm not sure what's going on.