Migration to new iMac, how to get Music (iTunes Match) to connect to hard drive library

Migrating from an iMac that could not upgrade past High Sierra. All my music is on an external hard drive, organized by iTunes on that computer. The migration to Music on the new iMac with Big Sur went more or less smoothly, until I realized that it was not 'recognizing' the music on my external hard drive that I physically reattached to the new iMac. Music app was fully populated with cloud references to my music. I have the Music Media folder location set to my external drive. It says all of my music is available to be downloaded. But I already have it!

A test download of 1 song put it in the correct place on my external drive, but it made a duplicate copy with a 1 appended to the song name.

Am I supposed to download an entire new copy of the library and throw out my existing one? All 26K songs, 165GB? Is there not some way to tell it to locate these files locally?

Really like to resolve this before I rip any newly purchased CDs into my library.