Can we fit an 11 speed cassette to new Shimano XTR 12 speed hub? I'm looking for a very silent hub. Upon searching, I came across with Onyx hubs which definitely has no sound. I really like it, but my budget doesn't. So I've searched a little more and found Shimano's new 12 speed XTR hub with Scylence tech which cost half the price compared with Onyx. My problem is, it's 12 speed with new Microspline freehub body. I have an old XTR 11 speed setup.

So there lies my question, can I fit an 11 speed cassette to a XTR 12 speed hub?

I know there's a spacer but I only see an upgrade from lower speed to higher like 11 speed to 12 speed not downgrade 12 to 11.
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.