Did you check network connectivety on the Pi when connecting KVM (Keyboard Video Mouse)?
Are you able to login on console?
Also check for below:
https://www.raspberrypi.com/documentation/computers/raspberry-pi.html#power-supply-warnings
Could search all of the systemd journals with below for "under-voltage" messages:
sudo journalctl --full --no-hostname --pager-end --grep voltage