I am not aware of anything else. NVidia NVENC might be an exception in certain scenarios. But I can't say that for sure.
I once read about an M1 patch for ffmpeg, which Handbrake probably doesn't use. With the patch, the video toolbox with ffmepg should be better. But the file sizes should still be a lot larger than with a good software encoder (although possibly better than without patch).
Unfortunately, since the usual tests only compare speed without considering file size and quality, many have completely wrong ideas about encoders. Many are not even aware of the problem. Many don't even seem to know that there can be quality differences and file size differences.
There are even people who are not even aware that there is a hardware encoder and believe that the CPU would be so incredibly fast. If you then compare a Mac with a Windows computer and only use the hardware encoder on the Mac, it is clear that it is much faster.