Windows opening quarter size

Greetings Jack PM,

Check out How to use safe mode on your Mac for another step to further isolate this behavior. Note that the creation of a test user account from "If the issue doesn't continue in safe mode" has already been completed suggesting that software for your user account may be causing this behavior. This article will also have you test safe mode, check login items and reinstall macOS if necessary.

If still experiencing this problem, use Get Support to investigate further with AppleCare support.

Regards.

Hello Jack PM,

Welcome to Apple Support Communities.  It sounds like you need some help with app screens on your Mac. We're happy to help.

Can you look at this thread and see if it helps?

How to disable automatic window resizing … - Apple Community

Cheers!

Hi Jack PM,

Does this only happen with third-party apps, or with built-in apps as well? Knowing this will help to narrow things down a bit.

We also recommend testing to see if you can replicate the behavior in a newly-created administrator account. Here's how to 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.

Click the Add button  below the list of users.

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.

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.

Enter a password for the user, then enter it again to verify. Enter a password hint to help the user remember their password.

Click Create User.

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.

Then, sign in to the new user account and test it out. The results will help determine if you have a system-wide or user-specific issue, which is good information for working out how to proceed.

Let us know the results. Take care.