With whirlpool going out of biz, what coinjoin is there for btc?
There's plenty for anybody who want to research. Coinjoin is a technique.
Doesn’t work when mempool fees are high
LN is disconnected from mempool, that's the entire point of an L2. Your transactions don't go on chain or in the mempool. Main chain secures the transactions, lightning stores the transactions. The main chain only stores the start and end balance of a lightning channel, that's it.
Most people are forced/nudged into using custodial wallets
Their choice, some people will always prefer custodial options no matter how easy non-custodial ones are. LN works fine non-custodially, that's how I use it. You move money from L1 to L2 in a single tx. Now you have a lightning channel that can have functionally unlimited transactions in it between you and anybody else on lightning. Transactions confirm in a second for pennies in fees.
LN was not designed to be a privacy tool. Bitcoiners tried to shoe-in that it is also a privacy tool
Privacy continues to enhance, look at the Bolt12 upgrades for example. But I agree, and Bitcoin can't hold a candle to Monero's level of privacy.
#shopstr is a growing alternative which uses nostr for posting instead of Facebook. Unfortunately not as many people but I always check there first and list there preferentially. You can use any payment method with is but most people use Bitcoin lightning, which has some privacy pros and cons but certainly more private than Facebook.