I don't pretend to understand what the Ukranian goals are here, but if you look at this incursion from Putin's viewpoint, it might change his calculus which I suspect has been "if I keep the 'special operation continuing, I probably get to keep my position (and my life)". Now he has to consider how having part of the Russian homeland under occupation changes that calculation. From my viewpoint, it makes his position more precarious - but I also don't pretend to understand Russians in general and whether this occupation might trigger some kind of uprising. I do expect there to be a lot fewer partisans in areas occupied by Ukraine than there are in areas occupied by Russia. Maybe none at all. Gotta wonder what the results of a referendum might be.
Just thinking it through...