Go to Photoshop > Preferences > File Handling.
PDF doesn't automatically open when saved | Mac OS
PDF doesn't open automatically when saved from Photoshop
When you save a file as PDF on Mac and enable View PDF After Saving in the Save Adobe PDF options, the PDF file doesn't open.
Solution: Disable background saving
Deselect Save In Background from the File Saving Options section.
Save your file as PDF.
When background saving is enabled, the command to open the PDF reaches Acrobat (or your default PDF reading application) before the file creation completes. By disabling this feature, you ensure that the command is not sent until after the file is created.