Thanks so much for the insight Howard! Based on that I formulated my workaround to just downgrade the Moove theme. I uninstalled the current Moove theme and installed and configured the one for Moodle 3.10 and it works now.
I can't say for sure, but maybe the latest Moove theme has an issue with the Accessibility Toolbar. The only difference of my account to the user with issue is that the Accessibility Toolbar is enabled for him.
I can't say for sure, but maybe the latest Moove theme has an issue with the Accessibility Toolbar. The only difference of my account to the user with issue is that the Accessibility Toolbar is enabled for him.