How strict is RyanAir on luggage SIZE?

[MrsBargain]

Hey everyone.

Going away this summer to Portugal & I have paid for
1x 20kg suitcase for one person
Then
3x 10kg check in bags

My question is regarding the 10kg check in bags, I naively thought as long as they're below 10kg that will be fine. But I've done some digging and can see RyanAir restrict the size (55x40x20cm)

How strict are they on this sizing?

I was just looking at some "cabin" suitcases and even they are too big 😩

Note; these are check in bags, not ones we will have with us on the plane in the cabin

Thanks for reading

They dont really care about the size for the checked in bags. They are strict with the bag size if you are taking it on board as there is limited room there

So what is considered the very best, holds the most bag /rucksack whatever that you can use as carry on luggage on Ryanair please ?