Possible bug: in Sonoma HyperKey works with capslock (for example: HyperKey-M to show Mail.app). I tried using fn as the hyperkey instead of the capslock, but that would not work. I have only recently began using the (great) HyperKey functionality, so I am not sure the problem is caused by something else, but I'd expect the function key to be available as a hyperkey as well (I do not use the function key/globe key for anything else). I use a regular apple keyboard, on a macmini M1. I also do not use the key in secure input mode,
BTT currently only supports capslock as hyperkey, it's not related to Sonoma. (would be good to allow other keys, but it's complicated)