Data file has tripled in size (Q Mac 6.6.0)

@magoodm To me, your screen shot when Quicken is running looks exactly like what I've seen from other users who have the Quicken data file stored on a cloud service. The contents of the Package shouldn't change whether it's running or not, nor should the file size. Mine does not. I know you said your file is on your local hard drive, but I really suspect it is not.

You said your data file is in your User folder… but can we go back over exactly where? You wrote above that it is in ""Macintosh HD/Users/my name. With Quicken running, do you have it displaying the file name in the title bar (above the Home/Reports/Budgets/etc. menu bar)? If not, please enable Show File Name in Menu Bar in Preferences > General. Now, Command-click on the little red Q to the left of the file name, and it will display a drop-down menu of the path to your Quicken file. From what you wrote above, does this drop-down show this:
   your data file name
   Documents
   Quicken
   your user name
   Users
   Macintosh HD
   your computer name

That is, in the Finder when you open Macintosh HD > Users > your user name, this home folder contains folders for Applications, Desktop, Documents, Downloads, Library, Movies, Music, Pictures and some others. Is Quicken a folder here? And inside that Quicken folder, inside its Documents folder, is that where you see your current data file? 

Do you use Dropbox or OneDrive at all on your Mac? If so, can you check the settings to make sure the cloud service is not set to sync the location containing your Quicken data.

I feel pretty certain that one way or another, your data file is being saved on a cloud storage service. 

I'm sorry, but I'm not a Dropbox user, so I'm not sure exactly how you can determine which folders on your Mac have been linked to Dropbox. I think you need to look at the Dropbox desktop application's preferences to see which folders are synced. I'm pretty sure you will find that your "Quicken Data" folder, or perhaps your entire User folder, is tied to Dropbox.

If you're doubtful of that, try moving your Quicken data file to a different location. Do it from within Quicken, using the File > Move To… command. You could move it back to Quicken's default location, which is inside your User > Library > Application Support folder. (There may be a Quicken folder in that location already; if so, place the data file inside the Documents folder in the Quicken folder.) Once the file is there, does it stay at the smaller size whether it's running or not, and does the Package contents remain unchanged when you launch and quit Quicken? 

Aha! It's the file security that does it. When I added a password to my test file, the size suddenly dropped by over half when I closed the file, and the package contents changed to match the first of my screenshots. So the file encryption must be doing a compression pass as well. Which makes sense - pull all those subfolders into a single compressed archive & then encrypt the archive.

It's interesting that the unencrypted data seems to be available on disk while the program is running.

@magoodm I wouldn't think the origins of your transaction data in Quicken Windows should have any bearing: a transaction is a transaction. If you write very long memos in every transaction and I don't, your transactions would occupy more space — but not enough more to explain a more-than 150 MB difference in file size. (If you had a 100-character note in every one of your 66,000 transactions, that would add only 6.6 MB to the file size!)

I don't know of any way to analyze the data in the file. Someone adept with SQL could open and poke around in the file, but you'd need to understand the file structure to make much sense of it.

The only other test I can think of would be to export your data as a QXF file and import it into a new file. This is sometimes used as a last-gasp fix for a data file with suspected corruption. You lose all your settings, budgets, reports, attachments, and account connections, but all your data is preserved. You could do it just to see if the new file size is similar to or significantly smaller than your current file size. If it's much smaller, then you'd need to determine if it's worth the work to re-set the new file up with all those lost settings, or to continue with your existing file when it's no exhibiting any signs of problems.