IMPORTANT: You must make sure your SP2019 server is properly configured to host apps, by following the MS documentation: https://docs.microsoft.com/en-us/sharepoint/administration/configure-an-environment-for-apps-for-sharepoint
Installation steps can be found below:
1. Download the required packages to your desktop
Download the Apps Foundation Package zip file and unzip it on your desktop.
2. Install the below package to your SharePoint 2019 server
a. Deploy the KWizCom Apps Foundation Full Trust.wsp package using the PoSH script from the extracted Apps Foundation zip file or by using the standard
SharePoint Add-SPSolution and Install-SPSolution commands.
3. Upload packages to your Tenant app catalog
a. As a Farm Admin, go to the “Apps for SharePoint” library in your Tenant App Catalog site.
b. Upload the kwizcom-modern-apps-upgrade-onprem.sppkg package from the extracted Apps Foundation zip.
After the package is uploaded you will see the following popup:

Click on the “Deploy” button to properly deploy it.
4. Go to your site and add the KWizCom Modern Experience On Prem a. Go to the site where you want to have the app and go to “Site contents”
b. Click “New” menu and select “App”
c. Click “From Your Organization” link on the left side:
