https://www.mangago.zone/read-manga/the_princess_imprints_a_traitor/ - this one fits perfectly
https://www.mangago.zone/read-manga/beware_of_the_villainess/ - ML is not a knight, but cute werewolf tho
https://www.mangago.zone/read-manga/the_way_to_protect_the_female_lead_s_older_brother/ - she saved him, but manhwa is on hiatus and we don't get much of their relationship afterwards
https://www.mangago.zone/read-manga/failed_to_abandon_the_villain/ - not exactly like you want, she didn't save him, but ignored him and he somehow got attached. He still is like "Master, love me plz" and he is yandere ╮( ̄▽ ̄)╭
https://www.mangago.zone/read-manga/wake_up_warrior/ - this one is harem and FL saved all of them. It's cute story and so far she didn't choose anyone. I recommend this one.
To be true I like them both, I like how foward Yustaf is while also respecting Ran's decisiond, but Lumiere is also such a sweet poppy like guy, I loved how he accepted their relationship.
In other words, I like how both of them, put Ran's happines over their own. So I feld bad for the one that was left and wanted to read one where the MC stays with someone of a similar situation like his (no status like crown prince, duke, etc which is usually the case)
As for me, I love them both. I knew from the beginning that Lumi was unlikely to be chosen, but even so, his relationship with FL is beautiful and it doesn't even need a romance in this case. Why are master-servant relationships so appealing?
His hair looks gorgeous by the way, I would read for his hair alone (≧∀≦)
I am in the mood for a story where the ml is like Lumiere from Viridescent Crown.
I want to read a story where the MC rescues the ML from a bad place and the ML who has nothing but his devotion and maybe some kind of ability builds up his status to stay by the MC side.
Preferably green or yello flag but red flag like possesive obssesive ML is ok.