Dear Mac53,
Good day! Thank you for posting in Microsoft Community.
Sorry for the inconvenience the issue caused in your environment.
For us to confirm the issue symptom in your environment, could you upload some related screenshots about "The Ondrive folder on the SSD is an alias pointed back to Onedrive on the Mac HD. This is leading to multiple problems. Adobe Lightroom will not import files from the MAC HD to the SSD as it thinks the files are on the same disk as the Lightroom images. They are not. Also the issue with Time Machine - it has suddenly run out of space as it seems to be trying to backup my entire Onedrive folder which I don't want it to do."?
Note: Remove any private information before uploading the screenshots.
Meanwhile, I'd like you to provide the version number of the OneDrive for Mac sync client and the Mac operating system you are uisng for our reference.
Thanks for your effort and time.
Sincerely,
Cliff | Microsoft Community Moderator