Hello Britgirl,
thank you for your suggestion. Actually, I already looked in the page you mention, but I only tried option #1 (desktop compositor). Also, I didn’t find in my logs the messages listed under “How to identify the problem”, but I might have overlooked them.
This time, I tried option #2 (Use EGL capture) and now my problem is solved: I can connect to the login screen too.
Many thanks for your help