i managed to put it back the way it was, i had to keep switching the setting on the tv from regular hdmi to enhanced to get about 5 seconds of picture at a time, and finally got an image back on the screen
then in my hubris, i thought 'what if i try hdr again' and caused the exact same problem again lol. this time even the regular/enhanced switching didn't work, so i had to boot it in safe mode (which i couldn't see on the screen). navigate the menu without any visual or audio feedback for what i was doing by remember where the menu options were. do that about 3 times. and finally it started again and i have given up on hdr for now.
still going to try a newer hdmi cable, and it's currently connected via a splitter so i'm thinking of changing it around so it goes straight into the tv and plug something else into the splitter. i don't know if that actually affects anything but i want my dynamic range to be high.