My Love Eundong features a MASSIVE amount of gaslighting (not within the lead couple but from others).
I second Save Me & try Delightful Girl Choon Hyang that’s a completely different tone from the rest but I definitely remember tons of gaslighting from the second leads.
The dramas focusing on parents making their kids live a specific way and place importance on values such as education or maintaining upperclass-dom like Heard it Through The Grapevine and Sky Castle also have pieces of this.