Is there an error message when the backup fails?
What is the full path to the folder that contains your Quicken data file on the hard drive and the folder you using for backup? Are you using OneDrive, Dropbox or Google Backup?
Again, what is the full path to the folder that contains your Quicken data file?
@John Carey I backup to an NAS (Network Attached Storage) drive on my network which is mapped as drive A. I have been doing this for 10+ years without a problem. As Greg-The Greek asked where is you Quicken data file (QDF) located on your computer? It should be in the C:\Users\UserName\Documents\Quicken\FileName.QDF.
I suspect that your data file might be corrupted in some way. When was the last time you validated your file?
I would then suggest you copy your data file if possible to a thumb drive and do a clean install of Quicken. There are I believe instructions on the web site for removing all traces of the old program and then reinstalling Quicken. I am assuming that you have a current subscription or else this will not work.
Before reinstalling Quicken, I would suggest booting your computer into Safe Mode with Networking and then trying to see if Quicken freezes.