Unfortunately things once have been easier. The first Tuya devices contained ESP8266 microcontrollers and had a vulnerability that allowed users to just upload a different firmware. But at some point they started using some cheaper microcontrollers that aren’t as easy to program. So there is no custom firmware available for many/most of the recent devices. Beware if the supported devices repository says “soldering required” or “module needs to be replaced”. I don’t know why they do this, but it requires a hot air soldering station and proper soldering skills.
Regarding Zigbee: I bought some Ikea stuff. The lightbulbs work fine. But I also had issues with the buttons.