Mark, BIAB added this option many years ago.

I believe a dim chord is by definition a dim5 (and a flatted 5 at that). Here's the thing: I have never seen 'dim5' anywhere outside of BIAB.

If you want a dim7, you have to write dim7. So in my opinion the correct way to set it in BIAB display settings is to say dim=dim5. It looks like you agree.
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BIAB 2022 Win Audiophile. Software: Studio One 5 Pro, Swam horns, Audition, Notion 7; Win 10 64 Pro. Hardware: custom i7 16 Gb; Roland Integra-7, Presonus Studio 192, Presonus Faderport 8, Royer 121, Adam Sub8 & A5X monitors