How stupid can you be... Well, let's be honest, I'm not stupid, but I sometimes overlook something, and sometimes I draw a conclusion too quickly. At first, I didn't see anything in Plesk, but I was completely wrong about that. Then I got so excited about it that I wanted to have something similar on my home server. I delved further into that. Conclusion: Plesk and by the way Cpanel must be excluded, because of the cost. There are free alternatives, but each package demands a "clean" installation of ubuntu 18.04. I pondered this for a while and then decided to take the plunge. Reinstalled the home server, again with ubuntu 18.04. That took a bit more energy than expected because the boot media was no good. And when the home server was running again, I put the TinyCP program on it. At first, it didn't work, some critical packages and PHP modules were still missing. I gave all kinds of instructions via the command prompt and then it still didn't work.... or...
That was a fun one! I had an SSH window open for both the home server and the VPS. That looks very similar! And "so" I gave a number of commands to the wrong computer, with my stupid head. On the VPS, the web server and the email were completely broken!!
Fortunately, Strato has an excellent backup procedure and I was able to restore the VPS to the situation from a few hours ago! Thank you, Strato!
Now everything is back in order. The VPS runs on ubuntu 18.04 with Plesk and the home server runs on ubuntu 18.04 with TinyCP. And it all works great!