https://www.mangago.zone/read-manga/the_evil_lady_s_hero/
https://www.mangago.zone/read-manga/another_typical_fantasy_romance/
https://www.mangago.zone/read-manga/the_male_lead_monster_lives_under_my_bed/
https://www.mangago.zone/read-manga/i_m_a_martial_art_villainess_but_i_m_the_strongest/ fits your bill but romance doesn't play a big role
https://www.mangago.zone/read-manga/the_heroine_had_an_affair_with_my_fiance/
https://www.mangago.zone/read-manga/i_m_the_ex_girlfriend_of_a_soldier/
https://www.mangago.zone/read-manga/i_ll_just_live_on_as_a_villainess/
https://www.mangago.zone/read-manga/why_she_lives_as_a_villainess/
https://www.mangago.zone/read-manga/beware_of_the_villainess/
https://www.mangago.zone/read-manga/pupillary_master/
https://www.mangago.zone/read-manga/i_became_the_wife_of_the_male_lead_bored_corona_kids_version/ kid ml is cranky at first but only for a little while & never toxic
Not exactly isekai per definition, but similar: also set in another world but with regression
https://www.mangago.zone/read-manga/please_marry_me_again_husband/
https://www.mangago.zone/read-manga/my_younger_brother_forces_my_flower_path/
https://www.mangago.zone/read-manga/honey_i_m_going_on_strike/
https://www.mangago.zone/read-manga/life_on_the_flower_road_of_the_grand_duchess/
https://www.mangago.zone/read-manga/the_duchess_with_an_empty_soul/
Looking for isekai manhwa but ML is actually SWEET and NOT toxic!!! LIKE GREEN FLAGGGS
Please and thanks!!!