Shifting the catalog to Dropbox

Catalog should not be in a folder which is really a cloud drive. DO NOT DO THIS.

Why don't you figure out what is really taking up space on your laptop's hard drive instead of thinking that LrC catalog is the problem?

I'm up around 3tb 

I recommend that you use Windows File Explore to show what files, folders, etc are in the hard drive, and specifically the LrC is in. Have the file extensions shown (not hidden) have the file and folder sizes shown. Take a screenshot if that and post in a reply. This so other members can get an idea on what is going on.

Some suspicions, and some items to see if they exist:

• Backup folder in wrong hard drive, that is on same drive as working catalog.
• Old backups that might no longer be helpful (you would need to look/decide)
• Several old catalogs that are from previous versions if LrC, before upgrades.
• Library preview folder for old unused catalogs (see above)

Also, in case it is in a different drive or other media, where do you keep your original photos?

Remember that Adobe does not recommend, nor support placing the LrC catalog on a network share, be that an actual Server, a NAS, or the Cloud. Some try this, but eventually the catalog gets corrupted.

Also note that while Adobe does state they support placing the photos on the Cloud, in troubleshooting documents, they contradict that and state that is problematic. Some have luck.

Also one wrinkle with OneDrive (yes I know, off topic, sort of). Some have automatic sync/copy with OneDrive in place for their catalog.Typically due to Microsoft trying to force use of MS accounts instead of local. Disable that, it eventually fouls up. If your Library path includes the words OneDrive in it, fix that.

'Some links on not putting catalog on network share:

• https://helpx.adobe.com/lightroom-classic/kb/catalog-faq-lightroom.html

Some links on space:

• https://mastering-lightroom.com/lightroom-space-part-1/
• https://mastering-lightroom.com/lightroom-space-part-2/

Do not put the catalog on DropBox.   It is best to keep the catalog (*.lrcat) file on your primary drive.   It is highly unlikely that your catalog file itself is that big.  Your cataloged but independent image files may fill that much space!

If it were me, I would buy an external drive.  Then, using Lightroom Classic itself, transfer files the files to that external drive.  Once the drive is installed and registered in LrC it is an easy drag and drop process.  

In one word- DON'T...

Catalogs often become corrupted when working from Dropbox - even if there is a local version on a hard-drive (necessary for LrC.)

"Offload" your photo files to a large external drive, or even run your Catalog from an external drive.

MOVING PHOTOS- 2 Methods

Move Your Lightroom Catalog | Laura Shoe's Lightroom Training Tutorials and Tips