Russia has around 1,500 to 2,000 troops in Transnistria whose mission is to garrison the Cobasna ammunition depots near the Ukrainian border, where around 20,000 tons of ammunition are stored.
At least I have not yet found news that Russian troops in Transnistria invaded Ukraine. If there is any action by the 1,500 to 2,000 Russian troops in Transnistria in Ukraine, it will be when the Russians are very close to Odessa. A Russian map that has been released indicates that part of the operation will come from Transnistria, but no evidence at this time.