Mikrotik devices have TWO bootloaders.
Which one is selected at boot depends on the exact way you are resetting it.
Did you try both ways?
https://help.mikrotik.com/docs/spaces/ROS/pages/24805498/Reset+Button
How to reset configuration
- Unplug the device from power;
- Press and hold the button > right after > applying power;
Note: hold the button until the LED will start flashing;- Release the button to clear the configuration;
BUT:
Loading the > backup > RouterBOOT loader
Hold this button > before > applying power, and release it after three seconds since powering, to load the backup boot loader.