TLDR: Try connecting to a variety your TVs? Seemed to fix the issue for me. I just updated my 2017 MacBook to 12.4 Monterey last night (May 20, 2022). I thought that I had waited long enough for Apple to work out all kinks, but I immediately had no ability to detect my second monitor, which brought me to this thread here. I went through the basic troubleshooting steps and was incredibly frustrated because one of the simplest options mentioned didn't even work (hit the option key to switch the Night Mode button to Detect Displays). As an additional step I decided to try connecting to one of our newer smart TVs. Although the USB-C to HDMI cable didn't work, I was able to connect with AirPlay. I decided that before I unload I bunch of money on a new monitor that can use AirPlay, I thought I'd try connecting to my oldest TV (15 year old Sony with an HDMI port but no wifi or bluetooth) and maybe move it into my office if it worked. OMG, now the HDMI cable is working! I took it back to the original monitor and BAM! Connected with no problem. So, I have no idea why this worked, but it did.