Okay, I've managed to boot my iPad into DFU mode, my mac recognized the device and let me restore it with latest public iPadOS and now everything's fine.

As I said, I've already tried this instruction, but once I was in restore mode, my mac stopped recognizing my iPad. I don't get any restore options on my computer. Additionaly after I leave the restore mode my computer still doesn't recognize my iPad which is pretty sad. Also, my iPad is now stuck on apple logo so I'm really hopeless now.