Where can I get a user manual for the new Mac Pro?

The manual is apparently not available yet.

Check back for the 13th, when the Mac Pro 2023 becomes available.

when published, it might have a lot in common with this one:

macOS User Guide - Apple Support

.

That infoirmation is already available, but a bit lightweight.

Configure your Mac Pro - Apple Support.

Readers are eager to answer your specific questions.

Available yet?