Idk if you already read this, but it perfectly fits what youre looking for
http://www.mangago.me/read-manga/akatsuki_no_yona/
older ones but masterpieces
http://www.mangago.me/read-manga/anatolia_story/
http://www.mangago.me/read-manga/basara/
modern, prince, would say no masterpiece but still good read
http://www.mangago.me/read-manga/private_prince/
http://www.mangago.me/read-manga/100_perfect_girl/
Right now I’m enjoying this
http://www.mangago.me/read-manga/seduce_the_villain_s_father/
You should read 'Light & Shadow' if you haven't. It's a masterpiece
Second manga i would recommend is 'Private Prince'.
I would like some completed romance (straight) that involves maybe a prince or princess or something with a bunch of chapters to keep myself busy during quarantine ლ(´ڡ`ლ)