I have SP 2019 setup and I cloned and generated the .sppkg file from the solution below:
https://github.com/pnp/sp-dev-fx-webparts/tree/main/samples/react-script-editor-onprem
I uploaded to the apps store of the site collection and chose to deploy to all sites. Now, on my Sharepoint Communication Site, when I try to add the web part, it does not show up in the drop-down. Is there any change I need to perform? I am new to Sharepoint development.