Same here. Since the project-chip repository is in flux, which SHA would work against iSO15 beta? What"s the format of the QR code? It changed lately from CH:... to MT:... what kind of VendorID+ProductID is currently supported?

After installing the iOS beta, you need to enable matter/CHIP support. Check the PDF referenced in https://developer.apple.com/documentation/homekit?changes=latest_minor&language=objc for details.