Set multiple images to Use Thumbnail RH 2019

Nope, as far as know. You can turn off and on thumbnails for the whole project in the output preset settings, but this will apply only to images that have the Use Thumbnail property set to Yes, which is specified per image. In RH2017,  you still had to apply an image style other than img to images that you wanted to use a thumbnail for, which was also performed individually per image. So, it's not that different in terms of applying thumnails to images. The approach in RH2019 definitely provides more possibilities, as, for example, you can have different thumbnail size for every image, while in RH2017 it was the same for all of them.