I'm working on support for the following plugins for automatically turning the printer on when uploading a print: TP-Link Smartplug, Orvibo S20, Wemo Switch, Tuya Smartplug, Domoticz, MyStrom Switch, Tasmota and Tasmota MQTT (along with PSUControl, which was already supported). If one of these plugins is detected, the Connect to OctoPrint dialog will have an option to "Automatically turn on the printer" using a configured plug. After sending the API command, the plugin will wait until the printer is connected to OctoPrint and continue uploading the file.
Here's a development snapshot of the plugin: CuraPackage for Cura 4.4.x. Download the file, and drop it into the running Cura application window (not into a folder!). Then restart Cura.
The above version also includes (hopefully) better discovery and better handing of timeouts and refused connections when checking the API key.
Edit: I have updated the link above.