"Can I use the XTR M9000 cassette on my 11-speed road setup?
Maybe. It should clear your spokes and fit on your 10-speed and 11-speed (with a spacer) freehubs, but your rear derailleur will likely be incompatible with the 40t cog. However, some clever folks have figured out that a longer rear derailleur B-screw can be a cheap hack to make it work."
I thought I'd already posted about that one?
"Can I use the XTR M9000 cassette on my 11-speed road setup?
Maybe. It should clear your spokes and fit on your 10-speed and 11-speed (with a spacer) freehubs, but your rear derailleur will likely be incompatible with the 40t cog. However, some clever folks have figured out that a longer rear derailleur B-screw can be a cheap hack to make it work."
https://www.cxmagazine.com/shimano-xtr-m9000-11-speed-road-compatible-questions