Take a deep breath. I too sometimes have difficulties because of the USB stick that I use, but in the end it succeeds. I too have an Omnia. Meanwhile, download the latest medikit from hbs (which is the stable firmware) and the relative verification file https://repo.turris.cz/hbs/medkit/omnia-medkit-latest.tar.gz and https://repo.turris.cz/hbs/medkit/omnia-medkit-latest.tar.gz.sha256, then you can move on to branch you prefer (hbk, hbl, hbd); for example I am now on hbk. If you propose to use the other branches for medikit (and not hbs), you get the result you tell me about and you cannot access the router.
- format the USB key in ext4, btrfs, fat32 or xfs (make sure through disk utility that the volume is clean, a logical volume a partition, otherwise it won’t work);
- copy both link files (version 4.0.3 hbs) to the flash drive and connect the flash drive to the Turris;
- hold down the reset button (behind the router) until LED number 2 starts to color (for a total of 4 LEDs lit);
- pay attention: the number of LEDs on must be four (neither 3 nor 5);
- wait for Omnia to restart; it will take a while and during the flash phase all the LEDs turn red; then it restarts again and all the flashes turn green and then turned on only wan, lan (if connected); for safety wait 3 minutes;
- with the computer connected via ethernet cable, try to access the address https://192.168.1.1.
- have fun!