That was the right idea !
While the registry changes brought no better result, I digged through the windows settings and hidden under 'Erleichterte Bedienung->Tastatur' (Ease of Access Control panel->keyboard ??) I found settings that work.
This is what I changed:
settings:
Enable "Aktivieren Sie die Wiederholungstasten, um wiederholte Tastenanschläge beim Gedrückthalten einer Taste zu verzögern"
and select time delays into the two appearig fields, I selected 0.7 sec for boths
This does not really solve the issue but it is much better now - occasionally only duplicates - will play a little with this settings.
By the way while testing, I have seen, that immediately before the issue appears the keyboard input is delayed by about 2 seconds and after that the letters (that were typed in the meantime) appear.
This 'freezes' did not change and I only see these, when KODI is running. And by the way, the registry changes were set to the old values after changing the keboard above settings.
The PC is a Nitro notebook with Core I5, SSD and 32GB Ram so, should be fast enough and I also have seen this on another PC (faster CPU, but only 16GB Ram) with WIN10 and also with WIN7 some years ago.
For me this is not really an issue because KODI is rarely runnig on the PC (only when managing the movie database or when there are thrilling news on TV. Anyhow this may point to a long existing issue because this happens only when KODI is started and with no other apps - even if 15 avidemux session are simulateously converting recorded Tatort movies from MPEG to h264 - which is really stessing CPU.
Something else also looks interesting: I tried to look into the live logs to check if something happens, when the 'freeze' appears using wintail (I use that from time to time for my work without ever seen it not working). For kodi.log this does not work (shows the end of the log and and stops though new lines are written) when opening the log with notepad++, wintail scrolls down to the new last line. (tried two older releases and also downloaded the latest WinTail-2.3.1.0-portable.exe) would be really interesting, what KODI is doing when the keyboard freezes.
Thanks for your help and if you think this should be investigated, feel free to contact me. I can reproduce this any time.
Gregor