Installing on MikroTik RB760iGS (hEX S)

I'm trying to install OpenWRT 22 on my device, I downgraded the firmware to 6.48.6, trying to boot via bootp and DHCP using the flash script on Ubuntu 20.04, I'm getting a DHCP discover and I see my computer offering an address, and it seems to send the file, but then it requests address and my computer sends a NACK, with a wrong network, then it boots to RouterOS.
Tried Windows with tiny PXE and there's nothing, tried to set the config from the web UI, using the reset button, using both bootp and dhcp (bootp doesn't seem to work at all), with backup booter set and unset.
I don't want to solder cables to get serial, so I wonder what I could do without opening the box?