How to restore full iTunes library in Apple Music after macOS 15.8 reinstall on iMac?

I have around 5,000 albums in my iTunes library backed up on several hard drives. Until I reinstalled OS 15.8 on my iMac there were no problems. Since the reinstall Apple Music shows only a vey small part of my iTunes library?

[Re-Titled by Moderator]

Original Title: After reinstalling OS 15.8 on my iMac, Apple Music is showing only small part of my iTunes library?