Is there a way to detect if Playcanvas can’t load/start or doesn’t work well (low refresh rate). Fallback or just a detection? Or another ideas?
You can run a quick benchmark within your app to work out the framerate on the device and then disable/enable certain features (e.g shadows, particle effects, LOD) to try and keep a higher framerate.
As for detecting WebGL, it’s something that you will have to put in the HTML page of the WebGL app. If WebGL is not detected, you can give the user a nice error message and/or forward them to another page. https://developer.mozilla.org/en-US/docs/Learn/WebGL/By_example/Detect_WebGL