What do you mean by "not Lightroom"? There is Lightroom CC (new program with old name), and there is Lightroom Classic CC (updated older program with new name). Which one are you referring to? Lightroom CC (now usually referred to as LRCC) is a set of new cloud-centric applications, there is a version for desktop, phone/tablet, and Web. Lightroom Classic is effectively the 7th version of the traditional desktop-focused application.
I'm assuming you are meaning the new LRCC app, but which platform are you wanting to export from? Watermarking is currently only possible using the phone/tablet application, and I think you can only select up to 15 images at a time to export. The desktop version has no such number constraint, but does not yet allow watermarks to be added during export.