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I have the same insulated drywall, and only a 20mm cavity between it and membrane covered brick.
The solution to hanging heavy shit is using a decent sized drill bit at angles to eat enough insulation away so you can then anchor flat against the drywall. As long as you’re careful not to open the hole wider than you want when angling the bit, it gives you a nice bespoke cavity to anchor in.
farfowl-
Yes, have tried that approach, I get a bit carried away at times though! The gripit undercutting tool is quite handy if you have a big enough hole https://www.screwfix.com/p/gripit-25mm-undercutting-tool/5333J?tc=IA6&ds_kid=92700048793290424&ds_rl=1249413&gclid=CjwKCAjwqIiFBhAHEiwANg9szom_q7AXyA8SCe-c2cU-ZwLZU5smsfbUYDm-b0PyYOLy5U7pedlixRoC7vcQAvD_BwE&gclsrc=aw.ds
Sam_w
My walls are weird! They are fully ranked with tanking slurry for a start. Fixing to the internal walls is pretty much impossible apart from in the most desperate needs. They are 900mm thick flint walls which have been heavily repaired over the years with just about every material you can imagine, so it’s pot luck what you hit. The walls are then tanked and have 100mm insulated plasterboard on top of that.