NATO must surely be watching the activity of Russian troops and fighter jets now even taking off from Belarus today during the war.
Times and descriptions here:
https://www.pravda.com.ua/eng/news/2023/01/20/7385755/
NATO must be ready to act swiftly against any jets used in Belarus and shoot them down if they are used directly in Ukraine.
Likewise getting some fighter jets to Ukraine from NATO and allies is surely needed quickly now if the above is the case.