No Startup Disk Options Appearing After Update

Tonight I tried to update iOS on my MacBook Pro from 2018. After half an hour of buffering, it came up with an error. I think the error said something like “there was an error with the update.”

It’s then taken me to this screen. For those who can’t see the picture, it shows an ask box with “Choose Startup Disk. Select the system you want to use to start up your computer.” Then further down an option to start in target disk mode. Behind all this I see another upload bar with the words “macOS Update Assistant.”

Now that issue is that after about an hour of loading, no disk options are available. I have tried resetting my computer, and it takes me back to waiting the half an hour, then takes me to this screen. I’ve done this maybe three times now. I’ve also tried going to target disk mode, but it’s clear that you need another computer to actually do anything with that. Lastly I’ve tried to exit the start-up desk screen and go to the Mac update assistant screen, but nothing will happen and update bar will not move.

Does anyone have any ideas what I could do?! I’ve tried R/shift combos and everything, and I’m getting quite desperate.