Hello Yusuf,
This error may be caused by a lack of permissions on the Add-On Explorer installer; the Add-Ons Explorer inherits the permissions of the MATLAB session. To resolve the error, try running MATLAB with elevated permissions and reattempt the installation once more.
If the issue persists, you may install the toolbox with the MathWorks Installer. The MathWorks Installer may bypass the issue causing the error message or provide more troubleshooting information on the error if the installation happens to fail again.
For more information on installing an additional toolbox to an already existing MATLAB installation, please refer to the following article:
Also, refer to this MATLAB answer link for further information:
Regards.