Have you read the BEST new-gen DARK FANTASY, ACTION SHOUNEN MANGA of the 2020s, the peak of human literature, Kagurabachi? If you're looking for a story with a more slow-burning pacing and world-building, but masterfully-written plot, realistically written and interesting characters with great designs, GORGEOUS ART that evolves with each new chapter, MOVIE-LIKE fighting choreography, BEAUTIFUL panelling and composition and NO ROMANCE, ZERO FANSERVICE AND ABSOLUTELY NO SEXUALISATION, ESPECIALLY OF IT'S FEMALE CAST!! OH ALSO IMPORTANT MENTION; DON'T DROP THIS AT CHAPTER 58 (IYKYK), TRUST THE PROCESS OF HOKAZONO-SENSEI'S GENIUS!! GO READ IT NOW!!!
https://www.mangago.me/read-manga/kagurabachi/ (PEAK FICTION)
Also these other shounen/seinen (mostly action, NO ROMANCE) mangas are great, too:
https://www.mangago.me/read-manga/gokurakugai/
https://www.mangago.me/read-manga/windbreaker/
https://www.mangago.me/read-manga/tokyo_aliens/
https://www.mangago.me/read-manga/gachiakuta/
https://www.mangago.me/read-manga/galaxias/
https://www.mangago.me/read-manga/ghost_fixers/
https://www.mangago.me/read-manga/centuria/
https://www.mangago.me/read-manga/psycho_eyes/
https://www.mangago.me/read-manga/witchriv/
https://www.mangago.me/read-manga/chainsaw_man/
https://www.mangago.me/read-manga/ultimate_exorcist_kiyoshi/
https://www.mangago.me/read-manga/madan_no_ichi/
https://www.mangago.me/read-manga/tongari_boushi_no_atelier/
https://www.mangago.me/read-manga/night_light_hounds/
https://www.mangago.me/read-manga/magical_girl_and_narco_wars/
https://www.mangago.me/read-manga/the_marshal_king/
https://www.mangago.me/read-manga/kai_hen_wizards/
https://www.mangago.me/read-manga/ruby_on_the_cake_hitogui_majo_no_bansankai/
Action manhwas with no romance:
https://www.mangago.me/read-manga/return_of_the_sss_class_ranker/
https://www.mangago.me/read-manga/superhuman_battlefield/
https://www.mangago.me/read-manga/my_disciples_are_all_big_villains/
https://www.mangago.me/read-manga/kill_the_hero/
https://www.mangago.me/read-manga/i_grow_stronger_by_eating/
https://www.mangago.me/read-manga/superhuman_era/
https://www.mangago.me/read-manga/even_the_devil_one_step/
https://www.mangago.me/read-manga/the_earth_savior_selection/
https://www.mangago.me/read-manga/castle/
https://www.mangago.me/read-manga/the_earth_s_chosen_savior/
https://www.mangago.me/read-manga/leveling_with_the_gods/
https://www.mangago.me/read-manga/i_regressed_but_the_world_didn_t_fall_apart/
https://www.mangago.me/read-manga/the_constellation_that_returned_from_hell/
https://www.mangago.me/read-manga/the_school_life_of_the_earth_leader/
https://www.mangago.me/read-manga/the_player_hides_his_past/
https://www.mangago.me/read-manga/the_evil_ring/
https://www.mangago.me/read-manga/the_fangs_that_pierce_the_heart/
https://www.mangago.me/read-manga/juvenile_prison/
Action/adventure [mostly FMC]:
https://www.mangago.me/read-manga/youjo_senki/
https://www.mangago.me/read-manga/joou_heika_no_isekai_senryaku/
https://www.mangago.me/read-manga/shinigami_ni_sodaterareta_shoujo_wa_shikkoku_no_tsurugi_wo_mune_ni_idaku/
https://www.mangago.me/read-manga/burning_effect/
https://www.mangago.me/read-manga/survive_romance/
https://www.mangago.me/read-manga/hand_jumper/
https://www.mangago.me/read-manga/hero_killer_1/
https://www.mangago.me/read-manga/delivery_knight/
https://www.mangago.me/read-manga/uglyhood/
https://www.mangago.me/read-manga/night_of_shadows/
https://www.mangago.me/read-manga/song_of_the_sky_walkers/
https://www.mangago.me/read-manga/devilshot/
https://www.mangago.me/read-manga/memory_merchant/
https://www.mangago.me/read-manga/karappo_no_shoujo_to_niji_no_kakera/
https://www.mangago.me/read-manga/majo_no_eden/
https://www.mangago.me/read-manga/maison_and_the_man_eating_apartment/
https://www.mangago.me/read-manga/little_girl_x_scoop_x_evil_eye/
https://www.mangago.me/read-manga/mononobe_koshoten_kaikitan/
https://www.mangago.me/read-manga/toshokan_no_daimajutsushi/
https://www.mangago.me/read-manga/usuzumi_no_hate/
https://www.mangago.me/read-manga/dungeon_nursery/
Here you go darling, hope some are new to you, enjoyyyy ヾ(❀╹◡╹)ﾉ~
Action fantasy recommendations with no romance