Hi @Elado,
Try to enable the Directory Browsing feature and add a default document in IIS:
Method 1: Enable the Directory Browsing feature in IIS (recommended)
To resolve this problem, follow these steps:
Start IIS Manager. To do it, select Start, select Run, type inetmgr.exe, and then select OK.
In IIS Manager, expand server name, expand Web sites, and then select the website that you want to change.
In the Features view, double-click Directory Browsing.
In the Actions pane, select Enable.
Method 2: Add a default document
To resolve this problem, follow these steps:
Start IIS Manager. To do it, select Start, select Run, type inetmgr.exe, and then select OK.
In IIS Manager, expand server name, expand Web sites, and then select the website that you want to change.
In the Features view, double-click Default Document.
In the Actions pane, select Enable.
In the File Name box, type the name of the default document, and then select OK.
More detail information, see HTTP Error 403.14 - Forbidden when you open an IIS webpage.
Besides, you could also check whether you have checked the related .NET Framework version, check the following threads:
HTTP Error 403.14 - Forbidden - The Web server is configured to not list the contents of this directory
Resolving the 403.14 error for ASP.NET on Windows Server 2016