What charity is the most impacting & worthy group of donating a small amount to every month?

There are so many, and so many people in need, that you need to be careful of the charity you pick.

I suggest this -

https://www.charitynavigator.org/

You can see ratings of various charities and see how much of the money actually goes to people in need and not to the people running the charity.

I donate a bit several that have special meaning to me.

pick a local volunteer run animal charity or most of your money will not get anywhere

NRA