Will upgrading to 64-bit cause my Picasa app to no longer function? Google is no longer keeping it uptodate

Then DO NOT upgrade to macOS Catalina 10.15 next month. DO NOT install anything higher then Mojave 10.14

And since you are on High Sierra right now, it would be wise to at least download Mojave BEFORE Catalina is release so at least you have the option of installing Mojave in the future. When downloading Mojave, it will start the install. You just Quit the install and you will have a copy of the Mojave installer in your Applications folder that you can use in the future.

macOS is already 64 bits. Catalina is going to stop working with 32-bit apps. High Sierra, Mojave and older macOS release can run both 64-bit and 32-bit.

If the Picasa owner will not provide a 64-bit version then you either need to find another app or not upgrade to Catalina or later versions of macOS.

32 bit apps will not run on macOS Catalina.

If you rely on 32 bit apps, then either find alternatives or don't upgrade to Catalina when it releases next month.

One more option. Run Mojave in a virtual machine (VMware Fusion, Parallels, VirtualBox) after you upgrade to Catalina and beyond. Just make sure you get a copy of Mojave before Catalina is released, as Apple has a habit of stopping to offer older version when the next version is released.

DCJudy wrote:

This did not solve my problem. I don't want to lose the ordering or label of my photos in Picasa.

Sure it did. You just don't like the answer.

Don't upgrade to macOS Catalina and you won't have a problem.