Wow yep this is not right. Enabling the hotkey should make it available.
I've looked back through the MMM versions and this has been broke since version 6.8 - August 2018!
Thank you for bringing it to my attention. I've fixed it (ddded as MMM_BZ14) it'll be in the next update, due before the end of the month. If your interested to know why...I checked the code and checking the box that is suppose to enable the hotkey does nothing...literately nothing - there is no code at all. I don't know what happened to it...but its back now.
I have a hack work around to fix it: it involves editing the mini mouse macro registry entries to force the hotkey to be enabled:
If your comfortable editing the registry, change these two values to True: Computer\HKEY_CURRENT_USER\Software\Turnssoft\MiniMouseMacroPro\Hotkey Playback Faster Enabled