They didn't rule on whether or not it was allowed but said the agency that objected to it didn't have standing and can't just object becase they found it offensive.
The 3 liberal justices were joined in the dissent by Justice Roberts who called it "likely illegal" and said Trump was exceeding his authority as POTUS and that just because he'd already demolished the East Wing it didn't mean they should allow him to continue. But 5 Conservatives ruled he can continue
We are so screwed, even the Conservative as hell Chief Justice thinks it's illegal but the other 5 still allow it?