I'm running Win 10 - BIAB 2021 (845) on both my desktop and laptop. When I put together a backing track on the desk top using Real Tracks and styles (pedal steel, fiddle, etc.) it plays back just fine but when I transfer it to the laptop, I get messages saying the instruments and styles are not there. I did notice that I didn't have the Real Tracks installed on the laptop so I downloaded and installed them but it really didn't help. How can I get both of my machines to be on the same page? BTW: I'm running the laptop version on an outboard 1TB hard drive.
Check where the required files are in your Settings. It's hard to tell where you are running the program from on the laptop.
If you still run BIAB from the shortcut laptop's drive, go into Options, Preferences, RealTracks and you will see a place to specify if the RealTracks are on a different disk drive. Then do the same for RealDrums. If you run the program now from the laptop, do the same thing and make sure you have the laptop drive as the location for the RealTracks and RealDrums.
To check that everything is OK, do Help, What Add-ons Do I Have. Make sure everything is showing up there.
Also, when you finish installing, please open the Style Picker and click the Rebuild button. Rebuilding makes your program search through your folders for what Styles and RealTracks are available. If you need to change the folders that your program is searching in for your RealTracks and Drums, please follow the steps in this video: