Knots? AFAIK ir has the same estimator as Core, haven’t noticed big differences in estimations. Maybe @Luke Dashjr can comment. Don’t also Sparrow Wallet have custom estimator?

a very useful correction here: https://nitter.net/mononautical/status/1725813952377127375 bitcoind does rely on the mempool for fee estimation. the estimatesmartfee algorithm works by tracking how long transactions in different "fee buckets" wait in the mempool before getting confirmed. which means it needs to see a representative sample in the mempool.

Only difference between Core and Knots fee estimates is Knots by default targets confirmation within 24 hours. Looking at your current mempool for fee estimation is broken by design