I mean, if you turn off WiFi radios, unplug from ISP, remove the antennas, and then reset with a single Ethernet connection, it’s really beyond the typical imagination to have the device still compromised. If you don’t trust it at that point, just get your own. Air gapping is the best you can do. So.. if you have access to a subterranean lair, take your laptop and modem/router down there (at least 50 feet). Then perform the reset.

Here is an attempt to get this right: 1. Turn off wifi on your router so no other clients can connect. 2. Connect directly to the ethernet port. 3. Issue factory reset. Do not reuse old admin or wifi passwords after reset.

depending on how compromised, the password might be visible. Also router dashboards usually communicate through http which is plain text password on the local network.