it may be a problem, but not necessary, depending what synchronised code does

no difference

only problme that with coroutines (suspend funcions) you always expect that this function will not block your thread. synchronised block may be very fast and not a problem, but again, as I said above, it depends what your synchronise block does

if you expect that synchronised block may block for long enough time, than better to use Mutex instead, or as simple solution, just wrap this function to IO dispatcher, so even if it block it will not be a problem for calling thread (especially if it’s Main thread)