I’m having similar issues and tried a lot of different things, which I listed on my question here: Cannot connect to Umbrel - #2 by cam.btc.
I’m going to get a HDMI micro cable so I can plug into my comp monitor and see what the Raspberry Pi is saying on it’s end because working in the dark is annoying.
The first thing you can try is to go to the terminal/powershell and type the command arp -a like that guide said. If the Raspberry Pi is on there its MAC address will start out with one of these configurations: Raspberry Pi Foundation <- MAC vendors list :: udger.com … and then just type in the IP in the browser.