Some do use teff, mainly mixed with other grains. It’s called Daafi in af soomaali.
The main difference between laxoox and injera is the fermentation period. Laxoox is usually fermented overnight or at best a day, whereas Injera is fermented over several days. Some families use and keep their premade sourdough starters.
In the northwest for exemple, Laxoox is usually made with sorghum, but can be mixed with other grains depending on what’s available.
Sorghum injera is also common among Ethiopians. It’s also the go-to grain in Sudan, like in kisra for exemple. Sorghum is the supreme East African crop.
Funny enough, I’ve always been used to laxoox that were slightly sour. So quite reminiscent of Injera without being the same.