Seen these sabre saw blades but having not used the sabre saw much and at 240mm long wondering would it bottom out on internal breeze block wall while cutting through from outside brick, Having used jig saws i do know they dont like cutting if the blade bottoms out? https://www.screwfix.com/p/bosch-s1543hm-brick-sabre-saw-blade-240mm/70198
house built around 1985 but until starting I don't yet know cavity width. thinking about it I could put couple lengths timber on wall first to take up the excess
You probably have a 50mm cavity, may just work. But I seem to recall a longer one been available although I can’t remember the manufacturer.