Maybe try that time i got reincarnated as a slime? MC really likes elves as comic relief i guess, but he technically had a harem "devoting" but he ended up not entertaining any one of them. Its more adventure tho, but its super fun to read and watch! But i guess he's aro not ace!
One Piece, i personally think its aroace friendly especially Luffy. Super long tho.
Tanaka-kun is Always Listless - tanaka is the MC and he literally just wanna sleep lol
Gekkan Shoujo Nozaki-kun's Nozaki - this is a romcom and i think nozaki is aroace, he had someone pursuing him which is always a failure lol , the anime/manga is super funny!
any manga/hwa/hua recommendations for a aroace mc? It can be any genre, just as long as there is good representation! (๑•ㅂ•)و