[GELÖST] Updated to gusto but getting error Call to undefined method Joomla\CMS\

Updated to tp-gusto theme but getting error : Call to undefined method Joomla\CMS\Application\SiteApplication::isSite()
php version 8.0
joomla version 4.2.6
Could you find solution

The package must be downloaded here with a valid subscription.
Then unpack and select the content of the Template folder (zip file tp_xxxxx) and install it in Joomla.

Template Installation

Please follow these steps:

Install the Astroid Plugin (Download)
Install the Template

1.) Download & Extracting

First of all you have to download the template package to your local HDD. Than extract the .zip archive. The archive includes the templates installation file and folders plus additional files like Photoshop source files etc. Keep in mind where you store the installation file and proceed to step 2.
2.) Installation

Log into your Joomlas admin backend (enter www.yourwebsiteurl.com/administrator in your browser) and click on "Extensions -> Install/Uninstall" to access the extension manager. Hit the "Search" button, select the installation file from your HDD ( please take the right Joomla template version - and hit the "Upload File & Install" button. Wait a moment and you are done. Proceed to step 3 to learn more about the activation and setup.

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How to install/update a template
www.joomlaplates.com/documentation.html