PHP error “Failed to open stream: Permission denied”

I am not a programmer unfortunately, and I was extensively browsing to find a solution to my problem – without success. I hope you might help me.
I want to create a webpage locally using Windows, Joomla4, XAMPP & PHP8. The installation worked fine and I installed a component to add content (JoomShaper SP PageBuilder Lite, SPPB). However, an article that includes SPPB-content cannot be displayed. This is the error from Apache Error Log:

require_once(E:xampphtdocscomponentscom_sppagebuilderparser./../helpers/helper.php): Failed to open stream: Permission denied in E:xampphtdocscomponentscom_sppagebuilderparseraddon-parser.php on line 20, referer: http://localhost/administrator/index.php?option=com_menus&view=items&menutype=mainmenu

I tried the following without success so far:

1. changing access rights of the helper.php and addon-parser.php files and all parent directories to 775
2. include ini_set('include_path', '.;E:xamppphpPEAR'); in the helper.php

I do not know what else to do or where the problem is located then.

Thanks for any help, greatly appreciated!
Bernd