It'll say on the instructions what the clearance needs to be but more is better.
Beats me that bldg control stipulate loads of insulation and then we go round cutting great big holes in it. So much for energy-efficient lighting!
Presumably mains downlights?
If 12V then the transformers get hot too so will also need room to ventilate.
Hopefully 12V are going back out of fashion now though.