Hi there, Folnjir.
I see that you're having problems syncing your iPhone XS with Finder since you've upgraded your Mac to macOS Catalina. Good job on the troubleshooting you’ve tried, and I'm glad to help.
About syncing your Mac and your devices -- Syncing your iPhone with Finder is different from backing up your iPhone.
Use the Finder to sync your iPhone, iPad, or iPod with your computer -- Review the information in this article on how to sync your iPhone XS. Be sure the music you expect to see on your iPhone is showing in the Music tab at the top.
Use safe mode to isolate issues with your Mac -- Since you aren't seeing the bar at the bottom showing you how much storage your iPhone has, restart your Mac in safe mode and see if shows now. If it works while in safe mode, reboot normally and test again in your own user account.
Let me know how that goes, and take care!