Quicken Mac won't Launch

Let's start at the end first. To access the hidden User Library folder, in the Finder hold down the Option key while puling down the Go menu; Library will be in the menu as long as you hold down the Option key.

If you do this often, as I do, there's a more permanent way to get Library not to be hidden. In the Finder, navigate to Macintosh HD > Users > [your User home folder]. With the home folder open, select View > Show View Options. At the bottom of the window which opens, select "Show Library Folder". (That option is only visible if you're in your User home folder.) Now Library will always be visible in the Finder's Go menu, without needing to hold down the option key. It will also be a visible folder in your User home folder.

Now, to the issue of opening Quicken while logged in as a different user: you don't need to re-subscribe to Quicken. But you do need to log into your Quicken ID. Instead of using a Guest user, I would use a different user account than your regular one. If you don't have one, simply go to System Preferences > Users & Groups, click the + icon, and create one you can call Testing or Quicken. Then log into that account and launch Quicken. If it prompts for your QuickenID, enter your regular username and password, and allow it to create a new file from scratch. When you're done, you can delete a temporary/testing User just as easily in System Preferences > Users & Groups. (I keep an account called Testing on my Macs so I have an alternate account ready to use whenever I need it.)

If Quicken works in the test user account, as you indicate it did, then that tells you something in your normal user environment is interfering with Quicken launching. The first thing I'd try is logging back into your regular User account, hold down the Shift key, and launch the Quicken app. Holding Shift at launch tells Quicken to open without opening your last-used data file. you should see a dialog box asking if you want to open [name of your Quicken data file]; press Cancel to allow Quicken to launch without opening that file. Does Quicken launch and have you land on the Let's Get Started page? If yes, we've found it's something with your data file; if no, it's something else in your User preferences.

If it fails to launch coding down the Shift key, I'd next try restarting your Mac in Safe Mode. To do this, restart your Mac and hold down the Shift key until it fully boots. In Safe Mode, and system-affecting utilities and extensions are disabled. Try launching Quicken now  and see if it launches or freezes. If it launches now and opens your file, then you know there's some system add-on at fault. (VPN? Firewall? Anti-Virus software? Other system extension?)

The other possibility is a damaged/corrupted Quicken preference file. I won't go into those at this point until you've eliminated some of the variables discussed above. Report back after you've tried some of these troubleshooting step and we can hopefully zero in on the culprit.