I updated to newest version with oneclick update and now i get the error: "
WARNING: …/web/piwik/core/Http.php(538): Notice - Trying to access array offset on value of type null - Matomo 3.13.6 - Please report this message in the Matomo forums: https://forum.matomo.org (please do a search first as it might have been reported already) (Module: CoreUpdater, Action: oneClickUpdate, In CLI mode: false)"
Matomo tries to make a HTTP request to fetch some data, but the response or status code is empty. But at the same time error_get_last() doesn’t return an error message which causes $error["message"] to not work, but throw the error you see.
The only thing I can think of is check if your server can make http requests to the internet (and maybe if you need to set up a proxy in Matomo)