Updated, 5.12.20:
Trump v. Mazars USA, LLP (consolidated with Trump v. Deutsche Bank AG) and Trump v. Vance overviews from SCOTUSblog (a privately-published blog about the U.S. Supreme Court).
Transcripts of the 5.12.20 oral argument: 19-715 Trump v. Mazars USA, LLP & Trump v. Deutsche Bank AG and 19-635 Trump v. Vance.