But its forces are side by side with the Baltics who are NATO members. If NATO attacks Serbia all bets are off. WWI stated because of Alliances. Well while Russia is a country, NATO is an alliance and the flipside of the NATO warning is true. An attack by one is an attack by all.
The Russians are fully engaged in Ukraine. What forces would they send against the Baltic states? If the Russians have to send untrained “Mobiks” to Ukraine, they don’t have anything they could spare for the Baltic states.
Serbia is nowhere near the Baltics. Please consult a map.