Can you recommend some stories that are on the shorter side (max. 20–30 chapters) and no...

MURMUR
run away with me girl
(both are GLs)

Stardust family,my reason to die,this witch of mine,footsteps in the snow

Thx but I know them already

Ty, doesn't my reason to die have 100 chapters

98 :')

I have others too if you'd like ......
Try mushishi,stalker,my broken mariko

https://www.mangago.me/read-manga/my_first_blue/
https://www.mangago.me/read-manga/echoes_of_footsteps/

https://www.mangago.me/read-manga/alter_ego_1/
sequel
https://www.mangago.me/read-manga/alter_ego_2_noel_june/