Very good dimmer switch. The family likes to use it in washrooms because it is completely silent to switch on. Since it is not integrated with ZHA, we dim it in the evening and manually set it to maximum power in the morning. Going to the toilet at night is not so blinding. If integration with ZHA would work, it would be possible to automate the lighting intensity.
The page you pointed says it works with zha.
Only on and off works. Brightness adjustment does not work.
I suggest you take a look at these issues, all of which mention this device.
The source code is here zha-device-handlers/ts0601_dimmer.py at fb5d256299dd789536034ca33a91afc646a07251 · zigpy/zha-device-handlers · GitHub
You will see DeviceType seems to be ON_OFF_LIGHT which confirms (to me at least) what you are seeing. In any event zigpy is not developed by Home Assistant, so your request is probably misplaced.
OTOH Zigbee2MQTT seems to support brightness in these devices.
https://www.zigbee2mqtt.io/devices/TS0601_dimmer.html
and the source code zigbee-herdsman-converters/tuya.js at 81712f36147b06d7b9cd29bafe0cedc2f25188a4 · Koenkk/zigbee-herdsman-converters · GitHub
A wholesale switch to Z2M would be a bit of a PITA, but a lot of people favour it for a number of (IMHO) good reasons.
Maybe we should move this topic elsewhere.
Without custom quirk, I have only on/off functionality and device property Quirk: zhaquirks.tuya.ts0601_dimmer.TuyaSingleSwitchDimmerGP
With custom quirk zha-device-handlers/ts0601_dimmer.py at fb5d256299dd789536034ca33a91afc646a07251 · zigpy/zha-device-handlers · GitHub I only receive on/off status and brightness level from device but can not control it from HA (property Quirk: ts0601_dimmer.TuyaSingleSwitchDimmerGP).
I will be grateful for any hint.