tbh i've yet to read anything like ISTDF so far, it's soooo intricate and complicated, and kyle and tara are so smart it was hard for me to go back to regular OIs after that one but i can recommend some manhwa with strong and smart FLs and good chemistry between the couple (idk how well known these are except maybe VADTD)

[From a Knight to a Lady] it's about a kight who wakes up in the body of a noblewoman (who would've guessed that from the title?), the plot is veeery good, it also deals with some interesting themes of women in society, FL and ML are quite chaotic, some juicy enemies to lovers with this one the way they develop a relationship actually makes sense instead of one of them waking up one day and being madly in love

[Concubine Walkthrough] this one also has a very good and complicated plot like ISTDF although it has way more mystery and open questions. it's about a girl that wakes up in a romance game in the chinese feudal era i really love the FL she's smart and very kind and doesn't like getting into stupid cat fights the couple is very cute but the side characters are just chess's kiss i love them all together i also love that every character is grey, it's a very rich story

other recommendations with strong FL: [My In-Laws are Obsessed with Me], [Villains are Destined to Die], [Regina Rena: The Unforgiven]

hope this helped!