OPTA Red and Blue Led Flashing MCUboot

Hello,
I´ve loaded the example sketch STM32H747_managebootloader.ino with arduino ide 2, and I choose to upload MCUbootloader with the default keys. Now everytime I load any sketch the blue and red led flashes and the Opta doesnt boot. I´ve tried to select Arduino Portenta H7 as board and load the same sketch with the option "signature+encryption" enabled but I have the same problem. I´ve also tried to create .pem keys with imgtool with this commands:

imgtool keygen -k ecdsa-p256-signing-key.pem -t ecdsa-p256
imgtool keygen -k ecdsa-p256-encrypt-key.pem -t ecdsa-p256
(I have a doubt that I have to create keys starting from the ecdsa... .h files contained in the example sketch, how to do this?)

then i`ve created a new .bin with following command:

imgtool sign --key ecdsa-p256-signing-key.pem --encrypt ecdsa-p256-encrypt-key.pem MY_input.bin MY_output.bin --align 32 --max-align 32 --version 1.2.3+4 --header-size 0x20000 --pad-header --slot-size 0x1E0000

and then i´ve uploaded all with dfutil command.

How to solve this issue? I would like to disable MCUboot and get back the default arduino bootloader.
Thank you
Daniele