I decided to download latest version and manually installed it on every computer at my classroom. It seems to work properly. I hope it will solve my problem. Honestly, I am thinking it was caused after some autumn update of windows 11. I is only my guess. Problem is, that I have cloned VEYON 4.9.0.0 on every PC at our school. So I will have to install it on every laptop and desktop again. Good think is, that the settings will stay the same like before. Sorry for my english.