Niche for donors

I have an idea for a money generating webpage where people donate to my charity project

I remember brook saying that if you are talking to everyone you are talking to no one.

So I know I need a niche, but I haven’t thought of the best niche yet.
I already have a Instagram page with 6000 followers in the gay/fitness niche. So I thought about using that as a resource/reach that I have already built. But, it’s perhaps not really the target market I am going for.
Other thoughts are:
People who want to make a difference but do not know how
Or people 25 to 35, social media savvy, socially conscious, who love being apart of project doing good in the world.
The thought that keeps coming up for me is that, “it’s hard to define a niche if It is for donating.”
Looking forward to your thoughts and advice