What is the minimum glide ratio of a motorized glider?
The minimum glide ratio of any aircraft is zero. Just put it into a vertical dive. Of course this is not sustainable; either you overspeed or collide with the ground.

in order to be certified as a powered sailplane (that is bureaucrat talk for motor glider), EASA CS-22.1 demands a ratio of weight to span squared of less than 3. The second limit is a maximum weight of less than 850 kg. That the code gives the maximum weight in Kilogramms and not in Newtons shows that the weight figure limit of 3 needs to be calculated with the mass of the aircraft, not its weight.

Initially, the criterium was a minimum sink rate of less than 1.0 m/s. That number was raised to 1.2 m/s when the first batch of glassfiber models could not meet that target. The mass per span squared rule came into force in 2003.

The defining criterium for an ultralight depends on the local rules and is a maximum take-off mass of 300 kg or less for single-seaters or 450 kg for two-seaters in Europe. Within the ultralight class there is no motorglider category.