I’ve tried different tracking methods, available in WP-Matomo.
I was able to create tracking-data with the settings:
tracking-code: js/index.php and position of java-script: header
But most likely that was not what solved my issue.
I think it is the ‘do not track’ feature in modern browsers like chrome.
When I tried creating data I once used FF and disabled the do not track feature in this browser.
Now I try to find the configuration in WP Matomo to deactivate respecting the do not track flag… debatable, but maybe helpful for the first.