It’s a huge leap from “gave money to United Way” to “support abortion”. I used to pay a lot more attention to organizations that made lists of abortion funders before I did research myself and found most of this is just not true or vastly overstated.
Given that many Catholic dioceses and Catholic Charities are United Way recipients, you could also say eBay “supports Catholicism” by that logic.
You are not culpable in any way. You buy something from me, you give me money I give you the thing. What I do with the money is not your concern or responsibility.
Exceptions would be actually doing business WITH planned parenthood or organizations that are engaged in actually doing abortions or the manufacturing of abortion-specific medical equipment.