@andreas-doehler May you please share the link to the logwatch docu? I dont find it either.
The logwatch.cfg goes to C:\ProgramData\checkmk\agent\config\
You may use globbing for the files:
C:\temp\SomeLog[1-9].txt
W Das System kann die angegebene Datei nicht finden
Note the space in front of the Classifier.
In ‘Agents and Plugins’ you find an example configuration.
Beside that I have this link to an old docu:
I hope that helps.