In the ON1 Photo RAW 2019.6 update, we updated the internet connection tool-kit used for signing into cloud services like Google Drive and Dropbox as well the sign-in dialog and other online content. This update solves several sign-in problems and is more secure. Unfortunately, this updated tool-kit no longer supports macOS 10.11. Apple recommends you upgrade to the latest available operating system.
Upgrading provides higher security and the correct drivers for devices such as your video card, which is what ON1 Photo RAW needs. These updates are free of charge from Apple and only require an internet connection. If for some reason you can not install a later version of the macOS, you should not upgrade to ON1 Photo RAW 2019.6. If you have already done so, you can re-install ON1 Photo RAW 2019.2 from the link below.