:) I am about to design my own T-shirt saying something like: Use GrapheneOS, make Google your underdog :) Anyways, do not underestimate the power of Google, it's got its tentacles everywhere... And if you think you are two steps ahead of it, it is already three steps ahead of you. Just saying, can't prove it (missing the technical know how), but likely true.
Now seriously, I would not hesitate for a second to buy a GrapheneOS T-shirt, even reveal my identity in support of it if all proceeds go to the people behind it.