Hello polonius2112,
Welcome to Apple Support Communities.
We understand that your iPad doesn’t finish syncing. We are happy to help.
Many times restarting can resolve many concerns. Please use the steps here to restart: Shut down or restart your Mac - Apple Support
"Restart your Mac
- On your Mac, choose Apple menu
> Restart. - If you don’t want app windows that are open to reopen when your Mac restarts, deselect “Reopen windows when logging back in.”"
After your Mac has fully restarted, please try syncing your iPad to see if the syncing will complete. We also would like to have you do some isolating troubleshooting steps—test in safe mode and new user account.
How t use safe mode: How to use safe mode on your Mac - Apple Support
"Apple silicon
- Shut down your Mac.
- Turn on your Mac and continue to press and hold the power button until you see the startup options window.
- Select your startup disk, then press and hold the Shift key while clicking “Continue in Safe Mode.”
- Log in to your Mac. You might be asked to log in again.
Intel processor
- Turn on or restart your Mac, then immediately press and hold the Shift key as your Mac starts up.
- Release the key when you see the login window, then log in to your Mac.
- You might be asked to log in again. On either the first or second login window, you should see ”Safe Boot” in the upper-right corner of the window."
How to add a new user account to test: Set up users, guests, and groups on Mac - Apple Support
"Add a user
- On your Mac, choose Apple menu
> System Preferences, then click Users & Groups 
.
If the lock at the bottom left is locked 
, click it to unlock the preference pane.
2. Click the Add button 
below the list of users.
3. Click the New Account pop-up menu, then choose a type of user.
- Administrator: An administrator can add and manage other users, install apps, and change settings. The new user you create when you first set up your Mac is an administrator. Your Mac can have multiple administrators. You can create new ones, and convert standard users to administrators. Don’t set up automatic login for an administrator. If you do, someone could simply restart your Mac and gain access with administrator privileges. To keep your Mac secure, don’t share administrator names and passwords.
- Standard: Standard users are set up by an administrator. Standard users can install apps and change their own settings, but can’t add other users or change other users’ settings.
- Sharing Only: Sharing-only users can access shared files remotely, but can’t log in to or change settings on the computer. To give the user permission to access your shared files or screen, you may need to change settings in the File Sharing, Screen Sharing, or Remote Management pane of Sharing preferences. See Set up file sharing and Share the screen of another Mac.
For more information about the options for each type of user, click the Help button in the lower-left corner of the dialog.
4. Enter a full name for the new user. An account name is generated automatically. To use a different account name, enter it now—you can’t change it later.
5. Enter a password for the user, then enter it again to verify. Enter a password hint to help the user remember their password.
6. Click Create User.
7. Depending on the type of user you create, you can also do any of the following:
- For an administrator, select “Allow user to administer this computer.”
- For an administrator, select “Allow user to reset a password using Apple ID.”
- Use Sharing preferences to specify whether the user can share your files and share your screen.
For information about Apple’s privacy policy, see the Apple Privacy Policy website.
If your Mac or Magic Keyboard has Touch ID, a new user can add a fingerprint after logging in to the Mac."
Let us know if you have further questions.
Take care.
