You said you installed ha on Pi. Can you hook up this Pi on a monitor and attach mouse and keyboard to it.
It’s not that hard to check does ha is up but you have to have access to computer weather this is physical access or remote access.
You can check what is listening on ports by
What are you using to access Home Assistant? A Windows PC/laptop? A mac? Your phone?
Could you find the IP address of this device and make sure it is in the same range (192.168.1.x)?
Why your device isn’t listed in the router’s page?
And have you tried to unplug your RPI from power and then power it again? Or maybe start the installing process again from the beginning? It shouldn’t take more than a few minutes.
Tried restarting home assistant?
Then verify it got the same address on your router (if possible, create an IP reservation on your dhcp server) and try to open again
Might not be the issue but be patient when starting HA the first time, it might take a while before you can reach it on http://192.168.1.128:8123 If possible attach a screen to the HDMI port of the Raspberry Pi and wait for the HA prompt to appear. Then you can browse to HA on port 8123.