Apply adjustment layer to a group

And another script here:

https://community.adobe.com/t5/photoshop-ecosystem-discussions/merging-an-adjustment-layer-to-many-layers/td-p/9571351

It should also be noted that right clicking on the layers panel and selecting export as will apply the adjustment layer to all layers without needing to "bake it in":

The whole idea seems problematic anyway as applying an Adjustment to several Layers together and applying it to the Layers individually does not necessarily yield the same result.

(edited)

@kornelijek – If I'm understanding you correctly, another option would be to duplicate the adjustment layer N times, with N being the number of layers in the group that need the adjustment applied. Then merge each adjustment into each individual layer, one at a time.

A script could automate this task, however, it would likely be very specific to the layer structure inside the group and wouldn't be very flexible.

You could select the group and adjustment layer and make it a Smart Object.  Then rasterize the SO to make it irreversibly.  Or you could leave it as a Smart Object just in case you want to edit it later.