Thank you @Lazarus for your answer! I hope it is indeed only soft bricked and recoverable as you say.
However, I have not yet found the way to repair it.
When using SP Flash, I always get error_msg: (cf the screenshot below) whatever I try (readback or download), including when trying to flash this Lunar OS image which I found in this post.
SP Flash terminal output:
com port clue: COM://.
scan device succeed, symbolic_link: COM:///dev/ttyACM0@/dev/[email protected]
connect brom START, connection options: , auth file: , cert file: .
connect brom failed, error code: -1, error msg: .
