I believe there is an "existing easy fix", in a form of a patch which is already applied to other stables. Unfortunately I lost track of the relevant fixes during the discussion so I can't point the relevant one.
The one you are after is 81e7c6befa36 ("of: dynamic: Fix overlayed devices not probing because of fw_devlink"). The revert went into 6.12.97 and 6.6.145 without it, which is why overlay probing has been broken on those two since.
Queued for 6.12 and 6.6, thanks for chasing it down.