I think it's more than just removing the one installed from the play store, I think you must also BLOCK the ability to install updates from the play store.  Not a big deal if QB is the only thing you are using the scanner for, but a mess if you need to have other things install from the play store.

My experience was, the app worked great after installing the APK from the link https://intuit.me/eswma (found at https://quickbooks.intuit.com/learn-support/en-us/help-article/install-products/setup-use-warehouse-... for about a day, then it updated the app from the google play store and scanning stopped incrementing the quantity again.

Next I reset the whole device back to factory, and then installed the app from the APK file, and NEVER SIGNED IN TO GOOGLE, and it is working great.

You do have to allow the installation of the APK in developer settings.

AND WHY is the APK different from the google play store app.  And why does the google play store app work fine on the TC20/TC25, but not the TC21/TC26.  Come on Intiut, DO BETTER!