Upgrading to Apple's release of iPadOS 15.5 will resolve this issue.
If you are unable to upgrade to 15.5, Apple's release of iPadOS 15.4.1 contains a workaround for the recent iPad issues in the meantime. You can solve them with the following steps:
- Update to iPadOS 15.4.1 (or higher).
- Open Settings and go to Safari > Advanced > Experimental Features.
- Select "Reset All to Defaults"
- Turn off "WebGL via Metal"
- Clear History and Website Data to ensure everything is reset. (Settings > Safari > Advanced > Website Data, then tap "Remove All Website Data")
Note: Following these steps will disable the Use Canvas/Legacy toggles on the device.