The screen shot doesn't show anything out of the ordinary. Neither does the other included info.
Can you try disabling the input by setting it to No Input and see if that helps or not?

And, do you have any digital connections to the M2 at all via the ADAT or SPDIF ports?

I don't know what is wrong so I'm asking general question trying to determine if there is a smoking gun or not.

I attached the Audition -> Preferences -> Audio Hardware screenshot.

Additional information from "About This Mac -> Hardware Overview"

Model Name: Mac mini
Model Identifier: Macmini6,2
Processor Name: Quad-Core Intel Core i7
Processor Speed: 2.3 GHz
Number of Processors: 1
Total Number of Cores: 4
L2 Cache (per Core): 256 KB
L3 Cache: 6 MB
Hyper-Threading Technology: Enabled
Memory: 16 GB
Boot ROM Version: 421.0.0.0.0
SMC Version (system): 2.8f0

About this Mac -> Hardware -> audio
M2:

Default Input Device: Yes
Default Output Device: Yes
Default System Output Device: Yes
Input Channels: 6
Manufacturer: MOTU, Inc
Output Channels: 2
Current SampleRate: 48000
Transport: USB
Input Source: Default
Output Source: Default

about mac mini -> hardware -> USB

M2:

Product ID: 0x0008
Vendor ID: 0x07fd
Version: 1.02
Serial Number: M20000018XXX
Speed: Up to 480 Mb/s
Manufacturer: MOTU
Location ID: 0x14300000 / 4
Current Available (mA): 500
Current Required (mA): 500
Extra Operating Current (mA): 0

System Software Overview:

System Version: macOS 10.15.7 (19H524)
Kernel Version: Darwin 19.6.0

Can you post a screen shot of your "Preferences>Audio Hardware..." dialog for us please? With the MOTU selected.