Cracks in L-stone - what is a shrinkage crack, what is a defect?

As long as no water gets to the reinforcement, the whole thing is actually just an aesthetic problem and can be fixed by filling it in. You will see over time if the part is actually broken and the steel starts to rust; a little filling won’t change that. It doesn’t look like that to me so far.

Not really.
Do I understand correctly that the cracks are on the 'pressure-opposite' side of the stones? That means the soil is on the other side?
Then in my opinion, they can basically only be settlement cracks, unless someone drove into it with the excavator.
If there had been too much pressure on the other side, the stone would have had to crack on that side as well.
Furthermore, the two cracks running almost parallel argue against a break. If the stone had broken in one place, it wouldn’t also break in a second place.
If you want to be absolutely sure, you probably need to have an expert prepare an assessment.
But that will probably be more expensive than eventually replacing the part if it really is broken.
My recommendation: just leave it be for now.
It’s not that great if an excavator rushes through your garden again.