The error message says you have already a process listen on port 5000. I don’t know what runs on an Ubunutu desktop on these ports. With Ubuntu server i had no such issue all the years.
This port is using the site Apache if nothing else is defined.
You can issue a “omd config test” and there you can configure the Apache port to some other value as 5000.
After the config change try to start the site again.