Can we fit an 11 speed cassette to new Shimano XTR 12 speed hub?
There seems to exist 11-speed microspline cassettes, meaning you can have a 11-speed drivetrain with a silent Shimano microspline hub. For example, here is a description I found at one webshop:

The special version of the XTR cassette is based on the 12-speed version with 10-51 teeth, but comes without the largest sprocket to offer enough space for the Wide Flange Shimano XTR FH-M9125-B rear hub (product code: 2278419) and thus for more stable wheels. &lt;...&gt; You even don’t need a special chain or a special shifting system, as the 9100 series shifters can be easily converted from 11 to 12-speed thanks to the Mode Converter. &lt;...&gt;
Details:
• Hyperglide+ cassette 11-speed
• For singlespeed and double chainring systems
• Can be integrated into a compatible 12-speed XTR system
• For Shimano Micro Spline freehub
• Compatible with Shimano 12-speed HG+ chains, such as Shimano CN-M9100 (product code 2273556)
• Material: steel, titanium, aluminium
• Aluminium spider (anodised)
• Incl. aluminium locknut
• Weight: approx. 299 g
Gear ratio: Shimano XTR 11-speed 10-45: 10-12-14-16-18-21-24-28-33-39-45 teeth
ATTENTION: Even though it is especially developed for the Shimano XTR FH-M9125-B Wide Flange rear hub, the XTR CS-M9110 11-speed cassette can also be mounted on standard XTR 12-speed hubs – losing the advantage of more stable wheels thanks to a wider hub flange.
ATTENTION: Only compatible with Shimano Micro Spline freehub. Not compatible with current M900 components and other Shimano 11-speed groups.

So the answer to your title question is &quot;yes&quot;. I am unsure from the description if you'll have to replace the shifter and/or derailleur as well in terms of how much the new cassette is compatible with older XTR derailleur indexing steps.