[Edit] I am having trouble getting a stock image of Raspberry Pi OS to boot on a Zero W. Using Raspberry Pi Imager 1.7 to flash the image onto a 32GB Sandisk SD card from a Mac M1.
After inserting the SD card back into the Pi and connecting an official power source, the Pi ACT light flashes in a strange pattern. When HDMI is connected, the display is black except for a faint, slow, regular flicker. I checked the LED Warning Flash Codes page but am still not sure what I'm seeing, it looks like "long-short-long" which is not listed.
If it is a partition issue, please let me know what I should do differently during the flashing stage. I have tried multiple different SD cards, and reformatting using the official SD card software as well as the RPi Imager "Erase" option.
When HDMI is connectedafter you boot? I would do the following. Flash the image onto the card. insert card into pi, connect hdmi, only now connect power. If you see absolutely nothing then try a different monitor, or try editing the HDMI configuration settings in config.txt file on the FAT partition which you should be able to do on your computer. You'll need to search for what each config setting does, though I believe the standard config.txt is fairly well commented.