On MacOS, pressing fn-up/down on a k380 sends brightness instead of page-up/down. This is behaviour is documented by logitech, but it's wrong - on MacOS, Apple officially documents that fn-up/down should be page-up/down. A similar problem exists for fn-left/right. According to Apple, these should be home and end. But on the k380, they select text. This is wrong.

Please either fix it in general, or allow users to rebind that. See apple's support page "Mac keyboard shortcuts" https://support.apple.com/en-us/HT201236