Happy End: I found out that Microsoft Rolled out Midi 2.0 via Update of Windows11. It seems that becuase of a bug the functionality of LoopMidi was blocked.
On my Windows11 computer I saw that a preview-update for Feb.-Windows-Update was available. Normally I do not install pre-view-updates for WIndows. But in this case I decided to install it and this pre-view-updated included a bug-fix fir Midi 2.0 @ Windows 11.
After a restart the virtual midi-interface via Loop-Midi was now shown again :-).
Maybe this information is helpful for other users which also use other tools for virtual midi interfaces via Windows 11.
@musicullum: Thanks for your fast feedback. Your analysis was absolutely correct. The Issue was not caused by VST live. It was caused by Windows 11 and a bug in a windows-update for Midi 2.0.
Wouldn’t it be possible that VST-Live could in the future also support virtual midi interfaces @ Windows 11? Then I could prevent an additional tool and could reduce the complexity of my system. I would assume that multiple user have use-cases were virtual midi-interfaces could be very benefitial.
Kind regards
Sascha