Due to changes in macOS, Adobe had to make changes while keeping PS platform consistent. Platform parity has always been important in Photoshop, for the sake of actions, plugins, tutorials, etc. When Apple or Microsoft changes their OS, Photoshop changes on both platforms. You need to choose Save a Copy if there are things in the PSD that are not supported in PDF.
Adobe changed Photoshop file menu Save As operation. Photoshop menu file Save As interface no longer support saving layered documents as Photoshop PDF or image file formats that do not support Photoshop Layers. To use Photoshop's document saveAs function to save those files you need to other Photoshop interfaces like "Save a Copy" that is a new menu File "Save a Copy" interface. Old Photoshop interfaces like Export As, Export Save for web and Photoshop Scripting these interfaces still support Document saveAs to save those file formats from layered Photoshop documents. Adobe only removed that support from Photoshop menu Save AS interface. Adobe also added menu File "Save a Copy" interface you can use to save those files. So use the interface that works best in your new Photoshop work flow.