When you are running Knots in Umbrel, then that might be the pitfall:
Discussion
I don’t use Umbrel, Linux, Raspberry Pi.
Have you checked this?
1) The "listening" flag in bitcon.conf is on?
https://github.com/bitcoinknots/bitcoin/blob/28.x-knots/doc/reduce-traffic.md
2) The rpi firewall does not block the port?
https://linuxconfig.org/how-to-enable-disable-firewall-on-raspberry-pi