I have seen no indication that Extrude has changed in any way, nor have I heard any other reports of any negative change in Extrude (I suspect we would have heard loud and clear if there had been a change of any kind).
I think you may be confusing the preview color within Extrude (and all body-creating features) with Combine. Extrude never showed a blue preview for Join. It always showed Join in the native component color. Here is Extrude:

The red outline you see there is normal profile selection behavior.
If there is an adjacent profile that is not selected, the border is shown as red:

again, that display has not changed in many years.
However, Combine does show a blue preview for Join:

again, unchanged for many years.
Both Combine and feature previews do show cuts in red:


again, not changed in any way that I can detect.
Jeff Strater
Engineering Director