@Dmitriy_La you can only use Mission Planner to flash the primary firmware. Make sure you are running latest Beta Mission Planner. I don’t think QGroundControl supports external flash flashing yet.
The firmware update mechanism is still fluid, there will be another update to bootloader soon for Primary to simplify firmware update process in latest 4.5 beta, this is the PR waiting for backport, if you want to keep track of progress 4.5 Backport Bootloader Fixes for H7 based devices by bugobliterator · Pull Request #27458 · ArduPilot/ardupilot · GitHub