Donrkebab,
The activation temperature of sodium silicate intumescent is about 110 – 120°C.
My understanding for fire rated lights is that as air temp at ceiling level increase, the metal fixing of light gets hot, and the intumescent material attached to the light expands closing the gap between lamp and ceiling.
For downlights the intumescent does not need any hot airflow through/past the light for the intumescent to expand.
SFK
So why did the op say "I checked online and found that they are NOT suitable to be covered with insulation".
Obviously the flow of air around anything depends on the shape, so depending on the design, the amount of hot gases needed for operation will vary. So there are possibly some that can be covered and some that can't, but these ones cannot be covered.