The best way to learn is to experiment.
As I told, I did the "Remove" tx through Electrum but it didn't really do anything.
The transaction was still there, unconfirmed.
I tried to make a new sweep, as sugested and the new transaction (with higher fees) simply replaced the pervious one.
Okay, it's more expensive, but at least I can get the rest of my sats !
I would still be interested in what you would have done in this situation.
Thank you in advance for your answers.
Best regards