Any straight recs we’re the male lead is muscular (bonus if he’s shy)
Some of these plots aren't that great, but here u go:
https://www.mangago.zone/read-manga/under_the_oak_tree/ (just a sweet couple with few insecurities and arguments here and there)
https://www.mangago.zone/read-manga/i_thought_it_was_a_common_isekai_story/ (he's muscular, tho not necessarily shy he is lovestruck at some point)
https://www.mangago.zone/read-manga/tamed_a_blackened_slave_man/ (this story aint ma fave fs but the ml's got muscles and the art is nice. He's not near shy tho)
https://www.mangago.zone/read-manga/in_the_doghouse/ (He has muscles but he isn't shy. Also has slightly more "hardcore" subjects rather than it just being cute and sweet)
https://www.mangago.zone/read-manga/the_lady_i_served_became_a_young_master/ (now TECHNICALLY the ml IS muscular in his original form. And he does fit the shy criteria at some point in the story. He just wont be in his original form for quite a few chapters, i think all of season 1 but i cant remember exactly)
Her adopted dad from from Korea is so fine I really wish she goes back to him though (I know most likely she won't but I can still hope)