I would definitely recommend "Stuck in My Sister's Dating Sim". its one of my personal 10/10. the mc was transmigrated into his sister's otome game as one of the villain with a major inferiority complex. his goal was to survival the game and find a way to return to his world, but along the way he managed to sway all the love interests of the game, which only give him extra headache. all of the characters are very well written and the plot with its world-building is well structured. its like the yaoi version of "my next life as a villainess"
another ones are, the Chinese novel "Scum Villain Self Saving System" by mxtx and a manga with the title "Ateuma Chara no Kuse shite, Supadari Ouji ni Choai sareteimasu" on bato
I hope this helps

if i had a dime for every story I've read about someone being isekaied into a novel or game as a side character and by accident makes the mc fall in love with them, i would have at least 4, which is weird