Toolbar selection error

Hi there,

We're sorry about the trouble experienced with Photoshop brush. We're here to help.

Which version of macOS are you on? DO you see this issue after the latest update? Did you try any troubleshooting steps, or does rolling back to the previous version resolves this issue?

Try to reset the tools followed by Photoshop preferences. 
Steps to reset the Tools and Preferences: 
To reset all the tools at once, right-click on the icon of whatever tool is currently selected in the Tool Options, select "Reset All Tools," and then click "OK." When you use the Reset All Tools option, this will also reset all the tool selections in the Tools bar to their defaults.
You may try to reset Photoshop preferences back to defaults and check if that helps. Here's the article for the steps: https://adobe.ly/3ceal5t 

Also, back up the Photoshop preferences if you have any custom brushes, actions, and workspace: https://adobe.ly/2vNz6FG. 

Let us know how it goes. 

Thanks,
Ranjisha