This is the actual reason this'll kick-off, regardless of all the posturing/sword-rattling that Russia will do to see how far the new US administration can be pushed. Crimea needs a fresh water supply as the Ukrainians cut-off the existing one (the North Crimea Canal), which supplied 90% of the total, back in 2014 and they're now running dry with it costing the Russians a lot of money to keep them supplied so, in their minds, they need to "confiscate" just a small section of land to get access back to this fresh water source and they'll use force to do so.
This fresh water issue has been known about, and reported about, for years.
I think that the above portion of Yellow area would be the prime target for any offensive, gaining control of the main fresh water supply, whilst showing military strength, shoring up home political worries and all over a small bit of land just 40 miles by 100 miles which the rest of the world won't fight over.
Of course the Ukrainians will fight back, and hard, which is why so much Artillery etc is being brought in i.e. stuff that has the range to fire from "Crimean" territory so gives Russia the excuse that it hasn't put troops into the "Ukraine" which everyone knows is a load of cobblers.