iOS Game Mode not activating

Recently Game Mode (iOS feature that optimizes cpu/gpu usage when playing games) stopped activating when I play Hearthstone.
I contacted Apple customer support, and they told me that implementing activation of Game Mode feature should be done on game developer side - this is the reason I’m writing this issue here. So my question is: is this a thing? Should we expect a patch that will bring back Game Mode feature? Or am I mistaken somewhere?
My device: iPhone 13 iOS 18.4.1