Got it working somehow.
I deleted the mmdvm_bridge4.service and re-entered again from scratch exactly as it was. This time it work no issue.
I have no idea what was the problem!!!
The only thing I can think of was my editor "nona" must have inserted some strange hidden characters or something. I have no clue.
root@xlx1:/lib/systemd/system# systemctl start mmdvm_bridge4
root@xlx1:/lib/systemd/system# systemctl status mmdvm_bridge4
● mmdvm_bridge4.service - MMDVM_Bridge Service 4
Loaded: loaded (/lib/systemd/system/mmdvm_bridge4.service; disabled; vendor preset: enabled)
Active: active (running) since Wed 2021-09-15 09:50:08 EDT; 3s ago
Process: 8955 ExecStartPre=/bin/sh -c echo "Starting MMDVM_Bridge: [`date +%T.%3N`]" >> /var/log/netcheck (code=exited, status=0/SUCCESS)
Main PID: 8959 (MMDVM_Bridge4)
Tasks: 2 (limit: 1148)
└─8959 /opt/MMDVM_Bridge4/MMDVM_Bridge4 /opt/MMDVM_Bridge4/MMDVM_Bridge4.ini
Sep 15 09:50:08 w3kit-xlx1 systemd: Starting MMDVM_Bridge Service 4...
Sep 15 09:50:08 w3kit-xlx1 systemd: Started MMDVM_Bridge Service 4.