(Sorry it's a bit late but..)
I'm (probably) not on the aplatonic spec but maybe I can help you with alterous attraction
I've read that alterous attraction feels different for everyone so my experiences might or might not align with yours
For me alterous attraction feels like
1. 'mm I would kinda like to date that person but I won't be jealous or hurt if they date someone else. Being their romantic partner would be nice, but for some reason being their friend is just as appealing'
and also
I don't feel butterflies when I'm with them
(For me, butterflies are always present when I feel romantic attraction. so if the butterflies aren't there, big sign that the attraction isn't fully romantic)
Or
2. 'Ummmm I definitely don't want to date them in real life but why am I feeling all these butterflies?? ;o; I think I would be jealous if they started dating someone but me dating this person? Ewww'
I dont know if you read it already, but here's a reddit post I read about alterous attraction