If you are looking for 64-bit FM synthesis without using FM8, consider these options: Arturia DX7 V

It retains the brilliant matrix-style modulation that made FM7 famous.

Before 2002, using FM synthesis in a DAW was cumbersome. You either owned a vintage DX7 (with its infamous "one slider" programming interface) or used generic MIDI modules. Native Instruments changed the game with FM7.

The Native Instruments is a legacy software synthesizer that is not natively compatible with 64-bit operating systems