By default the Ubiquiti EdgeRouter-X acts as a swtich, meaning packets from other ports will generally not be visible.

See the /sbin/switch command, in particular the mirror option:

/sbin/switch mirror monitor [portnumber]        - enable port mirror and indicate monitor port number
/sbin/switch mirror target [portnumber] [mode]  - set port mirror target; 0:off, 1:rx, 2:tx, 3:all

Monitor packets on port 2 from port 4:

# we'll monitor from eth4. (ports start at 0, left-most when facing)
sudo /sbin/switch mirror monitor 4

# start mirroring packets from eth2 onto eth4; a value of 3 means all packets
sudo /sbin/switch mirror target 2 3

Turn off port mirroring:

# stop mirroring packets from eth2 onto eth4; a value of 0 means turn off
sudo /sbin/switch mirror target 2 0

Note there are other options, such as calling tcpdump from ssh and piping the output to Wireshark from Windows:

ssh ubnt@ "sudo tcpdump -f -i eth0 -w -" | "C:\Program Files\Wireshark\Wireshark.exe" -k -i -

:: or

ssh ubnt@ "sudo tcpdump port not 22 -i any -w -" | "C:\Program Files\Wireshark\Wireshark.exe" -k -i -

ymmv, as ESP32 traffic was not actually observed with the tcpdump method. See also sudo tcpdump -D for a list of device interfaces.

For more details on the EdgeRouter-X, see this post.

tcpdump manual