Idex is potentially a decentralized exchange, but it also has centralized elements which make it something classified as a hybrid exchange.
I would now class IDEX as almost fully centralized. They used to be a hybrid, in that you still had to deposit your coins (albeit to a smart contract rather than a wallet), but you could still do so anonymously and without KYC. Now with their recent implementation of KYC, there are few differences between a fully centralized exchange - you still have to give up your privacy and you still have to give up control of your coins.
Unfortunately, this idea of decentralized is still very new and I am still yet to find a fully decentralized option that is reputable and useable.
As OSS mentioned above, Bisq fits the bill of being open source, entirely peer-to-peer trading, and never touching your coins. I've had a few experiences with using it, and it has (thus far) been smooth and free from any issues. It's biggest issue at the moment is lack of liquidity compared to centralized exchanges, but I'm hoping that changes in the months to come.
Unless there is a good KYC implementation, fully decentralized exchanges should and will never be allowed by governments due to AML reasons.
Governments trying to shut down a DAO would be akin to governments trying to shutdown bitcoin. Its decentralization, by nature, makes it censorship resistance. Bisq have a good document explaining it here:
https://docs.bisq.network/user-dao-intro.html