I’ve seen numerous posts about this bug but most are at least 2 years old. I managed to get to level 100 before encountering it.
26 August 2026, planned ride was elevation evaluation in Watopia. In the early stages of segment 2 of the grade the screen went black but the game still seemed to be running in the background but wouldn’t quit.
After a quick search on my phone I force quit the application, restarted the computer, selected a different course and was able to complete an hour and six minutes without further issues.
System is a late 2015 iMac running the latest OS and game versions. Zwift is all I use the iMac for.
What other system specs? No issues with overheating?
Try it with lower resolution and detail perhaps - that could be worth a try.
The other alternative is to try and fresh install MacOS Monterery. If you can afford it, might be easier to go for a newer iMac, or if you have a TV you can connect it to, the Mac Mini (M4) - this will probably need to happen in the future, eventually Intel Mac application support will go.
I haven’t seen other reports like this recently. If it’s hardware related there’s probably nothing you can do. If it’s a video driver issue your only option would be using OpenCore Legacy Patcher to install a newer OS. At some point you decide whether it’s worth the trouble of using the old machine that is years beyond its last software update. If it’s only for Zwift then doing a clean OS install is another option but that would be a shot in the dark.