How to stack pixel layers (what's usually called clipping masks)?

[eobet]

In Photoshop and Procreate there is a concept of a "clipping mask", which translated to Affinity Photo is a layer that only draws pixels on an underlying layer, and there's no restriction on how many of these you can stack on top of each other.

I know Affinity Photo has this too. I've found the solution on this forum before, but it wasn't intuitive and I can't find it right now.

Can someone tell me why the layer named IMG_7169 disappears when I drop another pixel layer inside of it or choose "mask to below" on the same pixel layer?

This "just works" in both Photoshop and Procreate, and maybe it also does in Affinity Photo, but I haven't been able to figure out how!

EDIT: Ok... not sure if I will find this post again, but for future reference (to myself if nothing else)... the order in which you place things matters!!! If I remove the mask, and then start stacking additional pixel layers it works (and I can put the mask back afterwards), but if I start stacking layers while the mask is there, then the crop symbol appears and everything disappears! In other words, any mask always needs to be at the top in the stack!