Sorry that you cannot save in Photoshop as you're getting an error message "write access is not granted".
Please checkout the steps below:
1) Try going to the System Preferences of the macOS, then to Security and Privacy and add Photoshop to the Accessibility under the Privacy tab. Also, grant permissions to Photoshop 2020 under the Files and Folders section. 2) Turn on the Legacy Compositing option in Performance preferences. Choose Preferences > Performance, select Legacy Compositing, quit and relaunch Photoshop. Let us know how it goes.