I understand that when you launch the Safari app, the app opens but no windows appear. Safari opens and works as expected in a different User Account. Apple Support was unable to fix it.
The fact Safari works in a different User Account suggests a corrupted file in one of several potential places. I have several suggestions that Apple may or may not have had you try, so consider the following.
Quit the Safari app if it is open. Safari menu > Quit Safari. If that menu is dimmed or "greyed out" just force Safari to quit according to How to force an app to quit on your Mac - Apple Support. Then, press and hold a Shift key while launching Safari from Applications, Launchpad, or the Dock. Release the Shift key when Safari opens.
That action causes Safari to open with no previously opened windows or tabs.
If the problem remains, continue.
Quit the Safari app if it is open.
Then, navigate to your User Library by typing the following in the Finder's Go menu > Go To Folder... field.
~/Library
Make it look like this
... and click the Go button. A Finder window will open. The files it contains are some of your User Account - specific files that could be contributing to the problem. Other User Accounts have their own User Libraries.
From there, your task is to find certain Safari-related files and drag them out of their locations and onto the Desktop. Each time you do that, open Safari again and determine if the problem is fixed or not. Quit Safari if it is not fixed, and proceed to the next step. Stop when it's fixed.
Open the folder named Saved Application State. Drag the file named com.apple.Safari.savedState onto the Desktop. Then, back out of that folder (use the "back button") which returns you to ~/Library or just repeat the same Go To Folder actions you did before.
Repeating the same general instructions, open the ~/Library/Preferences/ folder. In it, find com.apple.Safari.plist and drag it onto the Desktop.
That is as far as I'll go for the time being, but you should have the general idea. The worst thing that could happen is that you will be logged out of websites and / or have to provide login information or whatever other website preferences may have been affected, in which case you could always drag those files back into their original locations. Let me know if anything helps.
