Liquid Network afaik works only between 2 Liquid Wallets.
Correct.
CoinJoin is effort & also costs fees.
Not much effort is needed, there are user-friendly software such as Wasabi Wallet. The fee is relative low.
I think that my proposed solution is a new solution that does not exist yet.
Maybe, but IMO using BTC custodial isn't good solution.
Correct, it is not much effort with wasabi wallet, but it takes time (until the pool is ready) and any effort is more than no effort.
Yea, BTC custodials are never the perfect solution - but the best for wide adoption of anonymity. I know, this is not the prettiest solution out there. It is just one.