I have not been following this crisis as closely as I used to but from what I understand the recent heat up seems to be a bit more serious than annual/semi-annual "Russia is going to invade"
So Russia is saying Ukraine is amassing troops near Donbas, which means they will try to retake those regions by force, Russia of course cannot allow this and given Ukrainian army improvements and considerable help from NATO, including recent drones, would mean that Russia would not be able to support separatists with marginal support but will have to fully formally invade whereby plausible deniability is not feasible.
This is very similar to Russo-Georgian conflict over South Ossetia, in so far that Russia does not really have any incentive to invade unless Ukraine will try to take Donbas by force.
The lesson from Russo-Georgian conflict was that the US did not think that Saakashvili was crazy enough to attack separatist regions knowing they had the Russian backing. Results are known.
This time if Russia intervenes, the sanctions from the west-align economic bloc can do significant further damage and NATO support of Ukraine can ensure perpetual hot conflict to wither away the Russian economy.
Russia is essentially saying Ukraine is their red line, a hill that they are willing to die on.
So the question is, how feasible it is that Ukraine will try to retake Donbas by force? Is the Ukrainian military build up just political theatrics to bolster internal support or does this conflict has a possibility of heating up?
I hope this is just the annual/semi-annual sober rattling. They had been fairly frequent but this one feels a bit off compared to previous posturing.