I had a look at the spec but couldn't figure which ports actually support ADCs. I wonder if ADC() works for multiple ADCs. You are trying to look at ADC3. Can you try ADC(0) or (1)?

A pin-out diagram like:
https://mischianti.org/micropython-on-nucleo-stm32-stm32f411ce-and-stm32f401cc-flashing-firmware-and-basic-tools/#google_vignette
might help.

What happened when you tried my script?

adc = ADC(Pin('ENC')) # Hangs
I think some magic happens so that ADC() knows which pins are allowed.

Can you try ADC(0) or (1)?

Yeah as you can see in the video above, doing a number like that doesn't crash it. But...I don't know how that maps to what pin? I tried a script that runs through every ADC channel from 0-255 and they all returned 0xFFFF.

A pin-out diagram like:

What are you hoping to learn from it? It would take a while to create such a diagram. I can tell you that the pin I want to use is PB13. I've tried PB0 as well with the same result (crash/hang).

Datasheet: https://www.st.com/resource/en/datasheet/stm32g474cb.pdf

the pin I want to use is PB13.

That would be ADC3 input5.
Does Micropython even support using all three ADCs?
I seem to remember that a long while ago (and using a 32F4) I had to manually configure all that stuff on a register basis using either mem32, viper or thumb.

It looks like some work has been done to support ADC3 (seen above ^).

I was able to use Pin('A3') (ADC1_CH4) without issue. So I think you may be on the right track with there being something off with the ADC345 setup/clocking.