my main layer's weight slider is grayed out. the secondary's is set to -1 (!)

i found no mention whatsoever when looking on google about layer’s weight automatically set to -1 (when I press play. before that i can slide normally). Nothing on unity’s official documentation by the way.

also i found no explanation for the main layer’s weight slider to be grayed out.

I tried many many things but can’t get the animation clips on the two layers to work together like in this video