Oof, looks like they forgot to update the .pdsc file for the 5.8.x release. To bypass it, just rename the .pack to .zip, open the .pdsc file in a text editor, and delete the <file> tags for those two missing Kyber files. Re-zip it, rename back, and you're set. Navigating Keil's rigid pack manager is honestly as stressful as trying to keep the ball from flying off the edge in SL at max speed. If that's too much of a hassle, just pull the raw source files into your project instead!