Hello scardario, Backspace and Del seem to be working for me on 3.7.50-beta.
scardario yazdısometimes I have to double click on the main window to deselect whatever bone(s) I have selected to be able to select something in the Dopesheet
Do you mean that when you select a different bone, it doesn't change to said bone in the dopesheet? I tried to repro this too but it worked fine for me.
scardario yazdısometimes when I try to delete a selected keyframe from the Dopesheet it asks me if I want to delete another thing, like the current animation (with the Animations windows visible) or the attachment (with the tree visible).
This is due to the fact that you selected those things last, but then you didn't properly click on a keyframe to delete, but just moved the timeline marker instead.
scardario yazdıSometimes I'm not able to create a keyframe on the selected channel by pressing Ctrl+L (particularly with deformations on meshes or paths).
I tried to repro this too on stretchyman but it worked fine.
I'm afraid I will need more detailed steps/a gif or video of the problem, otherwise, everything mentioned seems to be working fine.