Have looked at the Report and kept it narrowed to and specific to Mail Loading Slowly.
There are some other issues which have been purposely omitted as they, IMHO do not fall in the strict perimeters of the main issue of this computer
Q - Description: Apple Mail is very slow to load messages
Q - Clean up - There are orphan files that could be removed.
A - Leaving Aspect of removed Application or extensions do not alway hurt the performance of the computer, they do not help to keep the computer in peak performance level.
Q - Unsigned files - There are unsigned software files installed. These files could be old, incompatible, and cause problems. They should be reviewed
A - Self explanatory and worth for the the User to evaluate the software on the machine for more up-to- date version or upGraded version.
Q - System modifications - There are a large number of system modifications running in the background.
A - Running modified OS, be it via Third Party Applications installed or remove or via User purposefully modifying the OS tends to have consequences including what the computer is experiencing now
Q - Runaway user process - A user process is using a large percentage of your CPU.
A - This could dovetail into User Usages and or outdated Third Party Application
Hardware Information: iMac (Retina 5K, 27-inch, 2017)
Drives:
Q - disk0 - APPLE HDD ST1000DM003 1.00 TB (Mechanical - 7200 RPM)
Q - disk1 - APPLE SSD SM0032L 28.00 GB (Solid State - TRIM: Yes)
A - This is a Fusion Drive, which was good in its’ day for extra inexpensive Internal Storage. But basically starting in Big Sur an above, the performance hit even with a 7200 RPM Rotational Drive will struggle to perform as the user expects.
Big Sur and above basically works way better with an ALL SSD Internal Drive
System Software:
Q - macOS Monterey 12.6.1 (21G217)
A - Heads Up - Dec 13, 2022 Apple Released an update version of Monterey to version 12.6.2
/Library/Extensions
Q - [Not Loaded] LittleSnitch.kext - at.obdev.nke.LittleSnitch (3.3 - SDK 10.8)
A - Unless this Application is properly configured for Incoming Traffic - it will negatively impact how Apple Mail will perform on Receiving e-mail
A - IMHO - this is the root cause of the Main Issue of the User - Slow E-mail Loading