iCloud Notes on MacBook Pro won't open. WebGL error

Error message is "Notes for iCloud can't open.. This browser's WebGL feature is not available. Try restarting the browser or try a different browser"

Running Mojave 10.14.5 with Safari 12.1.1 on a MacBook Pro

I have switched on WebGL 2.0 using the developer menu. I get the same error message. This has been happening for weeks now. Seems to be OK when I use Firefox but Safari is my default browser and as it's all Apple I'd hope they would work with each other.

Does anyone know the fix for this? Thanks in anticipation