Trying is the first step to failure...
For some reason Ubiquiti / UniFi doesn’t really love IPv6 after all those years. It took quite some time before the UniFi Controller itself supported IPv6. Beta IPv6 implementation started almost a year ago with the release of UniFi 5.7.7. But this doesn’t include the devices. Or at least not my Ubiquity AP-AC Lite. You can only configure IPv4 on the management interface.
A free tip for people with a (to new?) Intel I219V (Or Intel I219-V for search results 🙂