I’m not familiar with the ffmpeg options, but they’re documented on the ffmpeg.org site.
If you were using Handbrake, there are separate encoders for 10 and 12 bit. e.g. “x264” is the 8-bit encoder, and “x264_10bit” is the 10-bit encoder. So from the options in your profile, you can tell if you’re downconverting to 8-bit.
I wouldn’t be surprised if the ffmpeg encoder options are similarly selected. If you are wanting to be sure, configure the transcoding engine priority to use Handbrake with the 8-bit encoder in the profile and don’t use FFMPEG.