extremely slow sync from Mac photos to Lightroom CC

Hi - new user, but not a complete novice.

I have migrated a 40,000 Mac Photos library of approx 100GB from my 2019 iMac running MacOS 13.0.1.  I "sucessfully" migrated the library to Lightroom 6.3.1 on my desktop.  I say "successfully" because it shows 39,969 files in the library, but many of them do not have thumbnail images (many do).

My Mac is only 250GB, so with the system files, etc. it cannot hold both the Mac Photos library and the Lightroom copy held for migration.  I have a 2TB Scandisk Extreme solid state hard drive attached via USB where Lightroom is holding the copies of the library.

The end goal is to have all of the images synced with the cloud so my wife and I can access everything from both computers.  After 3 days, just 497 photos have synced in the cloud.  Lightroom is taking up 200+%  CPU usage but there is almost no network activity. Adobe Content Sync in the Activity Monitor shows just 392kb sent over the last half hour. The Data sent/sec metric in the Activity Monitor is bouncing between 0 and 10KB.

After two days, I have spent the day trying all sorts of combinations of things from restarting lightroom, restarting the computer, disconnecting/reconnecting the UBS hard drive, opening and closing Photos.  Bandwidth is generally very good, I have a home office "professional" setup for video conferencing and do not think bandwidth is the issue.

Is Lightroom spending three days to create the thumbnails of each photo before they sync?  Please help, this is cannot be working correctly.  Many thanks.