Good information for DEX, if this is accurate data then it is really an indication that users are increasingly turning to decentralized crypto exchanges which should mean that things are changing for the better.
Much of the volume will presumably be coming from DeFi altcoins being traded for Bitcoin or Ethereum due to the general bull trend, but it is encouraging nonetheless that people are using these services more. The more interest there is in DEXs on the whole then the more development and competition we will see in the DEX space, which is only a good thing.
In the event that a significant portion of the crypto market switches to DEX, do you think the authorities have an effective way to combat it in the sense that they require these services to take some action against their users?
I'm sure the authorities will try. Many DEXs still have a lot of centralized components to them - websites, servers, owners, etc. - so although you don't have to deposit your coins to a centralized wallet to be able to use them, there are still centralized components which authorities can act against, take down, sanction, and so on. Probably the best option for avoiding this at the moment is Bisq, as its structure is not unlike that of bitcoin itself. Although there are obviously core developers and websites, the trading platform software is ran peer to peer over Tor, and therefore very difficult to be shutdown
Specifically, if funds from terrorist organizations were transferred via DEX and also mixed via coinmixers, would that be something that would mean complete anonymity?
I'm not convinced there is such a thing as "complete anonymity", just as there is not such a thing as "complete security". Each additional step that you use - mixing, coinjoining, DEXs - makes it exponentially more difficult to deanonymize you (provided you are careful to not leak your data in other ways), but a significantly powerful and determined adversary could still manage.