I just don't see withholding of funding as construable as a law that abridges speech. I literally just re-read the first amendment and I don't see it.

It seems to be more on the spectrum of "freedom of reach". The same way a social media platform might not promote your content but doesn't take it down, the government is not creating a law about what institutions can legally say, just adjusting how much they're willing to support those institutions in other ways.