Red candy
https://www.mangago.me/read-manga/big_apple/ this one has secret agency stuff but I don't think it's the main focus, also another one is Penthouse XXX which also has secret assassin main character. Be warned that these have explicit sex scenes so if it's not your style then I wouldn't reccomend them
I have a few https://www.mangago.me/read-manga/madman_combo/
https://www.mangago.me/read-manga/shutline/
https://www.mangago.me/read-manga/heating_up/
https://www.mangago.me/read-manga/red_candy/
https://www.mangago.me/read-manga/dear_benjamin/
https://www.mangago.me/read-manga/outburst/
https://www.mangago.me/read-manga/the_origin_of_spices/
anyone have bls that involve spy, secret agent stuff