First, you are rotating on global y not local y based on the images. Rotating on local y would just roll the bone since local y is from the head to the tail of the bone.
Second, It is a gimble problem, not necessarily gimble lock. It has to do with orientation vs rotation or in other words the point you start a rotation vs the actual rotation. Reset all bones rotation. Goto gizmo drop-down icon(it’s to the left of the overlays icon. If I remember correctly it looks like a bow and arrow) check rotate and change default to gimble. Now when you click on the bone it will show you the gimble(true orientation) now both of your constraints are set to add so they add to owners own orientation. Now rotate both bones like before. Then click on owner to see how the gimble looks. Now do the final y rotation. It should follow the gimble’s y path. Hopefully that helps to see what is happening.
