You're correct, there is no comparison. The money Selena has earned is through her hard work to achieve the success she is today and she's got a great life, but has made the decision to pass along her experience with bipolar disorder along with the wealth she has to help without strings attached.
Harry and Meghan's "charity" is like an iceberg. The "top" they present is the benevolent uber couple that believe in a better world for all...blah, blah. Below the surface is the hard fact that they retain 95% of money donated for themselves and pass along 5% for their "causes". In addition, they make huge promises, but deliver little or nothing on those promises.
Dolly Parton ranks right up there as an excellent example of charity.