why i dont have a admin user?

If you cannot boot into Single User Mode (not Safe Mode), you can try to run the previously posted command via Terminal in Recovery: Start up your Mac in single-user mode or verbose mode - Apple Support

Once you have mounted the startup drive in Disk Utility as directed in the above-linked article, try removing .AppleSetupDone with this command in Terminal:

rm /var/db/.applesetupdone

Restart and it should run the Setup Assistant where you can create a new Admin user.

You can then use that new user to give your old user Admin privileges.

How did you get yourself here:

Did you try to change the name on an account?

Did you delete any users?

Did you acquire this Mac from someone else (i.e. it was not purchased new)?

With regards to other things stated here:

You don't have an admin user. It may have been deleted as you would not normally have a deleted users folder.

You are not sharing with anyone. Shared is a standard folder in /Users for sharing files between users on the same Mac.

You likely do not need to turn off FileVault if the above method works.