I am using BIAB2023.
BIAB does not currently recognize VST3 sound sources when playing plug-in sound sources.
For example, Toontrack's Ezdrummer2 is recognized and sounds fine, but Ezdrummer3 is not recognized.
I hope it will be improved in the next version upgrade or update.
Expect Ezkeys3 to be released soon.

Until there is native support you can try:
https://www.pgmusic.com/forums/ubbthreads.php?ubb=showflat&Number=754697#Post754697
All the VST3's will show the path as vsti3shell.x64.dll or vst3shell.x64.dll

This works in RealBand also and it still has the old Plugin Manager.
vst3shell_v1.2.1.zip
vst3shell_beta.zip
You can download from the source site but only use the 3 files with "x64"
https://www.xlutop.com/buzz/zip/
Extract the folder to anywhere outside of your VST2 folder.
Add vsti3shell.x64.dll to your VSTi list.
Add vst3shell.x64.dll to your VSTFX list.

In RealBand when you choose them you will get a list of your vst3's, pick one from the list.

It was confirmed that VST3 is coming next year / end of this year to BIAB.
Solutions offered by Musocity might work for now.

Yes, VST3 is planned for 2024 biab.

Is this available now in BIAB 2024 Windows? last time I checked it wasn't

Will BIAB 2024 Mac come with it when released this summer?

It's not available yet, but as you correctly point out, it is expected this year, probably in a forthcoming patch.

Did you look and see how the PLUGIN works in Reaper now allowing you to generate and transfer tracks instantly ?
You should have that in the Mac 2024 version and Reper has no problem using VST3.

Still no VST3 in BIAB. We needed it today:

https://www.pgmusic.com/forums/ubbthreads.php?ubb=showflat&Number=802047#Post802047