We also filed wife's I-751 in March 2019. The status changed to "Ready to be scheduled for an interview" in May 2019. We, then, filed her N-400 in August 2022. We had a combo interview on Dec 14th, 2022. She will take the oath in about 2 weeks from now.
You can keep waiting, sue USCIS, or file the N-400. I have heard that suing USCIS is expensive compared to filing the N-400.