I also state the exact same problem. It more or less seems to be an issue with “German” installations.
Well, fun fact, I tried to reset settings by running domain.de/wizard there I changed the locale to English US and walked through the complete wizard. With English setting I can paste times and they are shown correctly. Well is say for example Tomorrow 11:15 PM (Europe/Berlin) but I really putted 23:15 in German time. So it is displayed correctly.
When I wizard my forum back to “Deutsch” and pasting a new appointment with time … then the + 1 hour effect comes back again. (The times pasted in English setup are still displayed right).
So this does not seem to be a server time thing. Something seems to crash between localization of Europe and UTC.
Happy to test or give more advice if needed.
Running discourse in docker.
THX for further assistance!