Files I download on iMac are all associate with WinZip, which I have uninstalled

Open Terminal and run each of these one at a time

/System/Library/Frameworks/CoreServices.framework/Versions/A/Frameworks/LaunchServices.framework/Versions/A/Support/lsregister -kill -r -domain local -domain system -domain user

sudo /System/Library/Frameworks/CoreServices.framework/Frameworks/LaunchServices.framework/Support/lsregister -kill -seed -lint -r -f -v -dump -domain local -domain system -domain user -domain network

killall Dock

I understand everything you download has become associated with an app you do not have and no longer want. Is that correct?

Try this, as an example. Click this to download the Apple Platform Security white paper:

https://www.content.shi.com/SHIcom/ContentAttachmentImages/SharedResources/PDFs/Apple/apple-050521-AAW-Platform-Security-020221-ff.pdf

It's short; just a few pages. It should open in Safari. If it does not, stop right here and let me know what happens instead.

Assuming it opens in Safari, select Safari's File menu > Save As... and save that file to your Mac's Desktop or somewhere else where you know you can find it again.

Go to the Finder, single-click the file, and then File > Get Info.

Under General, the Get Info window should indicate Kind: PDF Document. Does it?

Under Open with: the dropdown menu should indicate Preview. Does it?