We had been waiting since March 2019. But, in Aug 2022, we filed my wife's N-400. 4 months later, both the I-751 and N-400 were approved during a combo interview.
Took 44 months to approve the I-751
Took 4 months to approve the N-400.
Both approved during combo interview on Dec 14, 2022
My wife will become a citizen in 3 days.
My advice is to file for citizenship as soon as eligible.