Coinjoin is a type of Bitcoin transaction where yours, and many other's, UTXOs are mixed and what outputs are many UTXOs of equal value given back to random individuals who put their coins in. You then have UTXOs that have an equal chance of belonging to one of the other inputs as they belong to you. Samurai wallet had a self custodial but centralized way to do this, and was working on a fully decentralized way before feds got to them. Moneros ring signature feature is similar, basically every transaction could be made up of one of 16 possible inputs. Basically a 16 user coinjoin by default in every transaction. What you're describing are coin swaps with no KYC swap sites, entirely different, but yeah a great strategy for privacy.