Today I updated to the latest version of Catalina on my iMac. When started on the new install, Topaz Studio 2 was not found by the system and I couldn’t find it on the disk, so I reinstalled it from my account. After reinstalling, I found that DNG image file associations had been changed to Topaz 2 as a default. I use Lightroom as my primary editor and Apple Preview to just look at files, and Preview has no problem opening DNG files. I don’t want Topaz 2 to come up everytime I click on a DNG file and I really don’t care for my system file associations being changed without asking - so I would prefer the installer not make this change automatically and since not everyone knows how to change file associations, I don’t think it should be the default.
You should raise a support request at the Topaz Labs website as this is a user to user website.
Just as an aside if the file associations weren’t changed on the previous OS version then it wouldn’t be changed on the new version. I would also check the Apple forums.
I am having the same problem…did you find the answer?