It seems, that it was the #Friendica daemon which started a lot of defunct #PHP processes, which caused my server to slow down with time. I have changed the setup to run the worker.php script every 10th second.

Thanks to #ChatGPT for writing me a #Python script, which could show me, which application had the most processes running and sort it by showing the one with the most at the top. With this script I could figure out what took up the resources.