Mine was also named "Apps from unverified developers". However, I'm not sure it actually got applied when I did it just now. Pressing on that quickly flashed something on the screen, but it disappeared before I could see what it was. I didn't get to flip a toggle nor enter the PIN. Pressing "Apps from unverified developers" again doesn't do anything now (not even the quick flash from the first time).

Appreciate any help!

EDIT: I restarted my phone just in case it did work, and checked again, the option is just gone. I'm unsure if this means something went wrong, or if it means it did work, and I'm currently in the 24 hour cooldown period.