Ok, i don't know exactly how chrome remote desktop works. But i'm guessing it's similar to TeamViewer where client connects to central server? In that case TCP connection goes only from client to internet server, but later desktop sharing can work in both ways. So you can't block TeamViewer only in one direction. If it works in different way with both sides starting (TCP) connections, then you would have to allow connections from internet to local network, and made an apropriate NAT rule as well. So you can block it simply by not allowing this traffic. However this would limit the use of application a lot. So I'd say it works similar to TeamViewer and you can't block it only in one direction. Just guessing tho.
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