When i look into the extensions catalog, i found the problem:
Autoupdate with extensions was switched on.
The recently updated monitoring extension was the problem:
2.4.1 (21 October 2022)
[!] Monitoring v2.4.1 will be the last Monitoring update that supports Plesk versions older than Plesk...
We had the same problem on several servers, without doing any updates. I found the solution on plesk server for windows.:
Look for this folder:
C:\Program Files (x86)\Plesk\admin\plib\modules\monitoring\vendor\composer
Open this file:
platform_check.php
Edit:
if (!(PHP_VERSION_ID >= 70400)) {...