A photohop's brush bug

@Francesco33659442hw24  In the first linked document are all steps exact described, point-for-point.

Scroll down to the "Reset Photoshop preferences" section. There are three differatn ways to reset the preferences:

• Using a keyboard shortcut on startup Photoshop
• Using the Preferences dialog when Photoshop is running
• Manually restoring your preferences 

All steps are described under the section.

I am not able to do one of the described steps.Thanks in advance.                                                                       

By @Francesco33659442hw24

One which step do you have issues?

Hi  @AxelMatt .Thanks for having replied to my message.I just want to ask you something related to your response:could you  make a screen recording of each step that you have described in your response?I am not able to do one of the described steps.Thanks in advance.                                                                                                                                                                  I look forward to hearing from you soon                                                                                                                                      Francesco Spera

In a first step you should try to reset the preferences of Photoshop using the steps described here:

https://helpx.adobe.com/photoshop/using/preferences.html#reset-preferences

It's recommended to backup your settings before resetting the preferences.

See here:  https://helpx.adobe.com/photoshop/using/preferences.html#backup-photoshop-preferences

If this doesn't help, we need more informations about your system.

Which version of Photoshop do you use?

Maybe you can post your Photoshop system info. In Photoshop goto Help > System Info and hit the copy button. Then paste the entire informations into this thread.