is that new or was it always in the Tos ??
I had some troubles in the past with poloniex due the same rule , so after they blocked Syiran IPs from even seeing poloniex charts I contacted bittrex and asked them if they are fine with Syrian traders
here is a screenshot at my very first day at bittrex, cause I wanted to make sure that things won't go wrong again
https://prnt.sc/h0wocqI don't know how new it is, but I have seen several Syrians complaining about being caught up in the recent account closures. If you have money on Bittrex and it's accessible then get it out while it's still possible.
They will be a lot more interested in keeping the US government happy than Syrian traders.