It's a strange decision of Tuya to not send an event when the button was pressed for more than 3 seconds, but only at the time when it is released
Here the 'held' type of button event is not the right one, but this is how it was implemented in the driver from the very beginning 1.5 years ago. If I change it from 'held' to 'released' now, it will break the existing automations for all those who are using the 'held' event at the moment. It should be possible to add an option / preference in the driver, although I consider this as a very low priority task.
This is hardcoded in the button firmware. Other TS004F devices will switch into dimmer mode by other key combinations.
There is no way to disable switching into the HE unsupported mode from the device itself. As a workaround, I could try to force back the 'scene' mode from the driver, as soon as the device reports it was switched locally to dimmer mode. I have added this at the end of my TODO list.. : )