Yeiiiiii finally i have found the solution.
I was using the BLEkeyboard library but not the correct one.
It’s available a modified library written for esp32c3 which makes the nimBLE mode to work properly.
I guess my seeed was already set to work in nimble mode in BT.
After changing the library, and after having installed on my phone the EFRconnect app, it’s now possible to pair without problem the board.
Super happy