SOLVED (kinda).
First, thanks @Scope666 for all their help. Turns out this integration is likely dead for new devices. Discovery is broken in some way that I can’t debug (at least for my pool pump switch). So if you’ve found yourself here looking for a way to manage your DEWENWILS pool pump, you cannot get THE VERSION I LINKED integrated. CHECK THE VERSION.
However, you can get THIS VERSION LINKED INTO HOME ASSISTANT. Be VERY careful that you buy the color version that says it links to either “Tuya”, “Tuya Smart”, or “Smart Life” Apps. These can all be integrated using the LocalTuya HACS integration.
Follow these instructions: SOLVED Tuya: Can't Link Devices By App Account: Data Center Error - #25 by Lostferret
And the instructions for installing & syncing devices for local Tuya.
Took me about 30 minutes to get working. Would have taken only 10 minutes if I didn’t have to troubleshoot getting a user onto the Tuya IoT site (see updated method for Android in the comment linked above).