Can't download on my MacBook Pro

I've used TT for years with no issues.  2 years ago I had to purchase a new laptop that would operate it, but I did and did fine.  This year, however, it won't even let finish the download.  The message I get is 

"There is no application set to open the document “Unconfirmed 691901.crdownload”.  I have done all the suggestions I found online to no avail:  I have cleared my history and cookies, deleted any previous TT versions, took down my firewall, restarted my computer, and tried a different browser.  Nothing.  I have also called TT and walked through it all with TWO specialists, who are stumped as well.

I see on some of the comments on here that some have had a problem with the new OS 15.3.2 (Sequoia).  That is what I have.  Does anyone have advice for me?  Is there an app I can download which will allow the download? Do I need to buy a another new computer? Try someone else's computer?  Help!