I believe this behavior is new to 26.1.0; i.e. it's been doing this for a while, and I suspected it could have workflow consequences only I didn't run up against it in real life until now.
Workflows or automations that manipulate history can break. Going back to a previous state to copy a layer style will now discard all intermediary steps. If one of those steps involves nested smart objects, one could easily throw away a substantial amoun of work by doing something that was harmless until very recently.
This has to be an error, as there's no user interface benefit nor conceivable use case for undoing a Copy Layer Style event (without bending over backwards to create far-fetched hypothetical situations).
This is on MacOS 13.6.7