Safari is not working properly after Mac golden gate 27.0.1 update

Before proceeding, how many times has the Mac been restarted since macOS 27.0.1 was installed?

The reported problems are that Safari sometimes does not launch on the first attempt, closing a split/partition can leave the Safari window unresponsive, and a window sometimes cannot be closed until it has first been resized. The first step is to determine whether Safari's restored session or an extension is contributing to the problem.

Quit Safari completely, then hold Shift while clicking Safari in the Dock. 

This prevents Safari from restoring its previous windows and tabs for that launch. 

Test whether Safari opens normally and then test the specific window operations that have been failing: resizing a window, closing a window, and closing a split/partition. 

Apple recommends this approach when Safari does not open or behaves unexpectedly: Apple: If Safari on Mac doesn't open a webpage or isn't working as expected

If the problem does not occur with the restored session bypassed, temporarily disable all Safari extensions under Safari >> Settings >> Extensions and test again.

If the problem persists, test Safari in Safe Mode. 

Since macOS 27 requires Apple silicon, shut down, Do Not use Restart,  the Mac, press and hold the power button until Loading startup options appears, select the startup disk, hold Shift, and choose Continue in Safe Mode.

If the problem also occurs in Safe Mode, create a temporary secondary user account in System Settings >> Users & Groups >> Add User and test Safari while signed into that account. 

If Safari works normally there, that would indicate that the problem is likely specific to the original user account rather than being a system-wide Safari or macOS problem. If the same problem occurs in the secondary account, it would indicate that the issue is not limited to the original user account.

To avoid a game of 20 questions   

Download the Application Etrecheck  ( External Link ) directly from the Developer.

This is a Diagnostic Tool that makes no changes to the computer.

It makes a coherent and readable inventory of both the Hardware and Software used on the computer 

The application is free or paid for added features. 

The Report will Not Reveal Any Personal Information. 

Post back the Full Report - Share Report >> Copy , then  paste  >>>> using the Additional Text Icon  <<<<

What you describe is not normal behavior for Safari on any version of macOS. Safari launches normally for me, and windows close when I close them. However, if you use the app in full screen with tiling, there are known issues on macOS 27 regarding the way Full Screen apps and switching/closing them with tiling/split-screen are handled.

Bugs should be reported to Apple here:

Feedback - macOS - Apple

For the issue opening Safari, have you rebooted your Mac? If not, that's the first step. If that does not help, then see if the problem is present when you boot in safe mode. That process performs some system cleanup and clears caches, and also disables 3rd party extensions that may cause problems.

Start up your Mac in safe mode - Apple Support

If that does not correct the issue, test in a new user account. A newly-created user account will have all settings at default, and if the issue does not occur in that new account then it provides guidance on what may need to be changed to correct the issue.

Add a user or group on Mac - Apple Support

Once the testing is complete, the new account can easily be deleted.

Delete a user or group on Mac – Apple Support

Those steps will help to isolate the problem.

It might help to download and run EtreCheck, written by a long-time forum member. The free version is fine. Post the full report using the Additional Text button. No personal information is revealed.