I run decarb with MgO under full vac at 70C and collect terps on a cold trap with dry ice.
You want to avoid oxygene while heating your extract as heat and oxygene will start degrading terpenes, promoting side reactions and what not.
I found the 70C to be the sweet spot. With 0.5g of powder MgO per kg of crude and 2h run time I get about 50% decarboxylation. Full decarb after another hour.
Going over 75C will introduce enough energy to start breaking more fragile terpenes and a well know “satan’s fart” notes will start to take over.
But ideally one would want to remove terpenes from freshly harvested biomass first. 35C under vac is perfect. It’s like stream distillation using water present in the plant but gentlier. And it takes 5-10 minutes to get most of the terpenes out.
Any fuckery with extracts, especially where high temp is required will affect the terpens. Remove them upfront and reintroduce later.
Make sure there is no water before adding MgO as this sucker will suck it and create very hard to remove turbocharged “limescale”.