This is a personal item size bag for under the seat. The max size on Ryanair is 24 liters. You are thinking of the cabin bag which is more like 44 liters. This Decathlon bag is great because it maxes out the personal item size really optimally.

I use the 32 L (https://www.decathlon.fr/p/sac-a-dos-de-randonnee-multi-poch...) as the "under the seat" luggage and it fits into the metal template.

I use the 32 L (https://www.decathlon.fr/p/sac-a-dos-de-randonnee-multi-poch...) as the "under the seat" luggage and it fits into the metal template.

Well, small cabin bag is now 40x30x20, so that 32l is too big: https://help.ryanair.com/hc/en-gb/categories/12489112419089-...

Hmmm. I flew last week and it was fine. They were checking most of the bags (they now have an incentive to find bags above the limits) and asked me to put mine in the metal case. It went in (reluctantly) and after shaking the whole device to get my bag out I was let go.