Mosquitto can't edit config file because of error? - raspberry-pi

Question

I completely installed everything fresh to a Raspberry Pi and installed Mosquitto. Many online instructions state that you should put listener 1883 and allow_anonymous true at the end of the config file /etc/mosquitto/mosquitto.conf to allow remote access etc.
But as soon as I put these two twos in the config file, Mosquitto won't start anymore? Somehow it also seems like no one else has the problem? I reinstalled everything and still nothing works. When I type sudo systemctl status mosquitto I get the following:
Loaded: loaded (/lib/systemd/system/mosquitto.service; enabled; vendor preset: enabled)
Active: failed (Result: exit-code) since Thu 2022-12-08 12:31:46 CET; 1min 50s ago
Docs: man:mosquitto.conf(5)
man:mosquitto(8)
Process: 630 ExecStartPre=/bin/mkdir -m 740 -p /var/log/mosquitto (code=exited, status=0/SUCCESS)
Process: 631 ExecStartPre=/bin/chown mosquitto /var/log/mosquitto (code=exited, status=0/SUCCESS)
Process: 632 ExecStartPre=/bin/mkdir -m 740 -p /run/mosquitto (code=exited, status=0/SUCCESS)
Process: 633 ExecStartPre=/bin/chown mosquitto /run/mosquitto (code=exited, status=0/SUCCESS)
Process: 634 ExecStart=/usr/sbin/mosquitto -c /etc/mosquitto/mosquitto.conf (code=exited, status=1/FAILURE)
Main PID: 634 (code=exited, status=1/FAILURE)
CPU: 91ms
Dec 08 12:31:46 MyPI systemd\[1\]: mosquitto.service: Scheduled restart job, restart counter is at 5.
Dec 08 12:31:46 MyPI systemd\[1\]: Stopped Mosquitto MQTT Broker.
Dec 08 12:31:46 MyPI systemd\[1\]: mosquitto.service: Start request repeated too quickly.
Dec 08 12:31:46 MyPI systemd\[1\]: mosquitto.service: Failed with result 'exit-code'.
Dec 08 12:31:46 MyPI systemd\[1\]: Failed to start Mosquitto MQTT Broker.
Configuration file:
# Place your local configuration in /etc/mosquitto/conf.d/
#
# A full description of the configuration file is at
# /usr/share/doc/mosquitto/examples/mosquitto.conf.example
pid_file /run/mosquitto/mosquitto.pid
persistence true
persistence_location /var/lib/mosquitto/
log_dest file /var/log/mosquitto/mosquitto.log
include_dir /etc/mosquitto/conf.d
listener 1883
allow_anonymous true
EDIT: I now changed the listener to port 1884. And now it worked. Could it be maybe, that the Wi-Fi-Router does have some settings where it blocks every Port on 1883 or something?