First, welcome to Band-in-a-Box and to the forum!
Open the RealTracks Picker and (1) use the Rebuild & Fix button and (2) Check "Show RealTracks That Are NA".
IF a bunch of RealTracks show up NA then you need to check the RealTracks folder setting.
You also need to use the StylePicker to rebuild you styles list as many styles demonstrate specific RealTracks.
The illustrations are from Band-in-a-Box for Windows since I don't have Band-in-a-Box for Mac.
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Jim Fogle - 2022 BiaB (922) RB (Build 4) Ultra+ PAK
Cakewalk - Zoom MRS-8 recorder
Desktop: i7 Win 10 build 2004, 12GB ram 256GB SSD, 4 TB HDD
Laptop: i3 64bit Win 10 build 21H2, 8GB ram 500GB HDD
Music at: https://fogle622.wix.com/fogle622-audio-home