audio midi setup - no 24 bit option?

I'm hoping you can help me! I have a 2018 27" iMac running macOS Big Sur. I'm using an integrated amplifier for a desktop listening system. My integrated is a Primare i35 Prisma. I'm running USB from my iMac into the Primare, and generally stream music from Qobuz or play FLAC files from my computer. The Primare DAC is capable of accepting up to 32 bit 768kHz inputs.

My question is that Audio Midi Setup on my iMac is only giving me the option to select 16 bit or 32 bit as the options. There is no option for 24 bit. I don't really understand all the details of sampling rates, but in searching the web it seems that most other people have a 24 bit option.

I've just selected 32 bit as the default and so far it sounds just fine. Should there be a 24 bit option available, and if so, how do I get it to show as an option?

Thanks for your help!!