Hi spatel_30,
I apologize for all the trouble it has caused and sorry about your time.
As per your description, using "CTRL" and multi-select files to upload from local folder to SharePoint online document library does not work. However, use drag files/folders from your computer to upload them to your SharePoint team site is work.
Based on my test using “CTRL” key to select multiple files does not work when I upload files in SharePoint online classic experience. Could you please confirm does users use classic experience? If yes, please click on “Exit classic experience” and click on upload button to see the outcomes.
Also, please try to use another browser on your machine and see the difference.
I just tested form my side and when I select “Upload” button in SharePoint online document library to browse to location and I use “CTRL” key to select multiple files and I’m able to upload file as expected in SharePoint online library. For reference: Upload files and folders to a library
If the issue still persists, please tell us more information below to let us help you:
1.Does issue happen to specific document library in SharePoint online.
2.Does issue happen to another user in your organization with same document library.
3.Confirm your browser e.g., Microsoft Edge, Google Chrome etc.
I appreciate your patience and understanding.
Best Regards
Waqas Muhammad