Any help with this would be greatly appreciated!

Hey guys! So long story short, I purchased 2 old Mac minis and some small touch screens to create a pair of wall mounted Apple HomeKit dashboards. I upgraded both to Sonoma (after multiple failed upgrades), but accidentally allowed the Mac to update itself to Tahoe (it would give me a notification like every day and I stupidly decided to give it a try). It resulted in a mess of a OS, and I did some even stupider tinkering in finder and somehow “deleted” the hard drive trying to reset it. I effectively have no OS whatsoever, and regardless of the key combination I use, which OS I try to download, my internet connection, or anything, I can’t get past this screen.

The only other screen asks for a firmware password which the prior owner swears to have no knowledge of whatsoever.

I was thinking of purchasing a disk copy of MacOS X and an old Apple disk reader, do you think that’ll work or is this thing ruined. Seperately, if anyone knows of a touch driver that’s cheaper than UPDD (I love their free trial but don’t have $125 to blow atm bc I’m not in the best place rn).

I welcome any and all advice!!

Thank you!