The Musca-B1 Keil pack contains a board support package.
The Musca-B1 Board Support Pack is available here.
The Trusted Firmware-M (TF-M) Middleware Keil Pack is a derived work, based on the publicly available, open source project: https://www.trustedfirmware.org/
Keil Middleware Packs generally require a suitable Board Support Pack for the relevant platform.
Note that Musca-B1 BSP does not work with earlier versions of the TFM middleware pack.
The TF-M Middleware Pack is available here.