I can confirm that the API to retrieve camera snapshot is not working anymore with Basic Authentication in 2023.1. There is nothing specific called out in Domoticz Release Notes, so I’m looking at what has changed in the source code and if there is a workaround.
Additional point on “Allow Basic Authentication over plain HTTP” setting. Depending on your setup, it might need to be enabled for authentication on any Domoticz API. For example, my Domoticz test instance is behind Nginx reverse-proxy, so even though it is going through HTTPS, when it’s proxied to Domoticz it is always as a local non-HTTPS.