What would be the potential thrust of an "electric jet" like Lilium's?
They look like 15 cm fans, thrust of which is competently ROM-ed in this answer.: about 40 to 60 Newton.

Note that the $C_T$ in the equation depends on fan solidity, the higher the number of blades and  the wider they are, the more thrust they produce, but also the higher power required. For a given fan power (and battery life) it makes more sense to increase fan diameter and decrease fan solidity.