Ok, I was able to replicate my issue on another lab, and, I was also able to fix this.
For the TL,DR; there is a missing zone in my lab local.lab, the lab part is missing, I need to create this zone and then create a DS record inside this new zone.
Once done, I was able to add my “new” DNS forwarding zone in IPfire with DNSSEC enable.
I will add more info later.
Nikos