throw them a curveball & recommend this
https://www.mangago.me/read-manga/after_being_shown_unimaginable_pleasure_by_an_orc_for_so_long_i/
If your friend is already OK with BL stuff, and don't have a repulsion/ aversion against two boys being a little fruity, then I would recommend something like
"Killer Crush" as it's funny but still good and serious at times.
"1995 youth report" (18+) It's cute and has a bit 90s vibe to it.
"Run Wild/ SaYe" about two boys finding each other, recovering from their broken households.
However, some people are subtly having internalised homophobia and feel wierd about two men loving each other.(And go, "this is not how men behave irl") In those times you can recommend them something which has BL tag but still has a romance subplot thing and also has other stuff going on.
"The Summer hikaru died" It's also psychological and there's no PROPER romance even though the MC is gay, and his "friend" also might be queer.
"Global examination" Great plot and not just cheesy romance.
"Murderous Llewellyn's candlelit dinner" is a good one as well.

I wanna recommend my friend a good beginner’s yaoi, preferably full color and not super complicated. Any ideas?