Here are some semi-hidden gems
https://www.mangago.zone/read-manga/yuki_to_matsu/ (Edo period)
https://www.mangago.zone/read-manga/ginza_neon_paradise/ (WWII)
https://www.mangago.zone/read-manga/baraou_no_souretsu/ (War of the Roses England; It’s never tagged as BL but is BL, it’s just very plot-focused and the MC is a gay intersex man)
https://www.mangago.zone/read-manga/ai_towa_yoru_ni_kizuku_mono/ (French Revolution)
https://www.mangago.zone/read-manga/a_proxy_painter/ (Georgian era)
https://www.mangago.zone/read-manga/gerard_to_jacques/ (French Revolution)
https://www.mangago.zone/read-manga/bidou_wakadanna_koi_shitau_wa_koushoku_otoko/ (Edo Period)
https://www.mangago.zone/read-manga/j_no_subete/ (1950s USA)
https://www.mangago.zone/read-manga/momo_to_manji/ (Edo Period)
These 2 aren’t strictly historical but are secondary world with no magic/supposed to resemble an existing era:
https://www.mangago.zone/read-manga/hyakujitsu_no_bara/ (Inspired by WWII)
https://www.mangago.zone/read-manga/barbarities/ (Inspired by enlightenment era France)
U can look here...
https://www.mangago.zone/home/album/162710/
Here historical yaois -
https://www.mangago.zone/home/mangalist/1145913/
Any historical bls (not mainstream ones)