Problem with files after migrating Dropbox from old to new Mac (with OS Sonoma)

Hi! I recently bought a new MBA and migrated my dropbox files from my old MBP to this. Unfortunately, I was told that the harddrive cannot accommodate all my files,  so I was asked to choose files to download to my new Mac, this despite the HDD of both Macs are of the same size and the newer Mac being an M3 (vs Intel). 

Now I have two major problems:

a) my new mac cannot include the documents file in the backup

b) I have to go online to access the rest of the files that I was not able to include in the migration. 

 

I assumed that with the migration, I would have a copy of all the Dropbox file listing in my new MBA, even though some of the files were kept online (not being synced). 

 

Question is how do I resolve both issues? Right now I am depending only on the MBA’s time machine to keep track of changes in files, and am hampered when trying to access other files in my Dropbox in my new Mac. 

 

Thanks in advance!!