https://www.mangago.zone/read-manga/one_step_from_hell/ teacher x student
https://www.mangago.zone/read-manga/eto_irokoi_zoushi/ (not school, but late teens)
https://www.mangago.zone/read-manga/dragon_s_first_crush/ dragon x crown prince
https://www.mangago.zone/read-manga/the_god_of_pain_s_groom/ late teen x god not much of school but the uke is a highschooler
https://www.mangago.zone/read-manga/geu_kkeute_issneun_geos/ student x student (uke's soul got switched)
https://www.mangago.zone/read-manga/augs_law/ this fits your description the most
https://www.mangago.zone/read-manga/aoao_waiting_to_be_eaten_caught/
Sorry 1st one is wrong
Sorry 1st one is wrong
https://www.mangago.zone/read-manga/ayashi_no_hakoniwa_ni_ukabu_tsuki/ it is supposed to be this
looking for a bl thats basically supernatural elements with school life and fighting or taking care of evil or daily life of demon hunters has to be urban