Compatibility list for FP421E (FortiAPs)?

Hello everyone

We still have some FP421E active which are managed by a fortigate. We are aware that those are end of support, end of sale, end of everything...

Unfortunately I have difficulties to find an official (old) compatibility list with these FortiAPs listed, to find out how far I can update the managing fortigate in order to have those FP421E (on 6.4.9) still being supported (fortios wise) so that we can prepare the fortigate for newer FortiAP models...

So far in the compatibiilty lists I found the only legacy models mentioned are the FAP221 and FAP223, but no FP421E...

Anyone an idea where to find something official?