Yes, this did the job!
my dietpi-services_edit.conf looks now like this:
[Unit]
#Description=PaperMC (DietPi)
#Documentation=https://paper.readthedocs.io/
[Service]
#SyslogIdentifier=PaperMC
#User=papermc
#WorkingDirectory=/mnt/dietpi_userdata/papermc
ExecStart=
ExecStart=/usr/bin/java -Xms1g -Xmx2g -jar /opt/papermc/paperclip.jar --nogui --noconsole
[Install]
#WantedBy=multi-user.target
So to who can I write to correct the incorrect doc? (Gaming and Emulation Software Options - DietPi.com Docs)