This is the solution that worked for me. I contacted Bandai Namco support about the issue and they quickly found out that my GPU drivers needed a clean update, so I did that and the game runs perfectly now.

This solution may cause issues with your PC, so if you're fine with the compromises offered by other fixes you may want to go for one of those instead.

Download Display Driver Uninstaller[www.guru3d.com] and use it to completely remove your graphics drivers and related software. You should set it to restart after the clean to avoid potential issues.

For NVIDIA GPUs, go to the GeForce Drivers page[www.nvidia.com] and input your GPU and OS information. Download the driver at the top of the list and run the installer. Go through the installation process, you shouldn't need to restart your PC.

Open Steam and run the game. Go into the graphics settings and set them to whatever you want, load a save or start a new game, and you should find that the stutter is gone.

This is a bit of a compromise as it will lead to a slight reduction in visual quality, but I've heard it work for some.
Start the game, and go to the options menu, then go to the graphics settings.

Change Anti-Aliasing to "Off" instead of "FXAA". It's implementation is supposedly buggy.

Set the frame rate cap to 60 or 30. The game was designed to run at 30FPS and may have issues at higher rates. Also disable VSYNC.

Make sure the game is running in "Fullscreen", as "Windowed" or "Boarderless Windowed" can cause more lag.

If you still want anti aliasing and V-sync, forcing them via NVIDIA Control Panel supposedly works better than the in-game settings.

Start the game, go to the options menu, and set anti aliasing to "Off".

If you don't have it already, install NVIDIA Control Panel. On Windows, you can get it via the Microsoft Store[apps.microsoft.com].

Somewhere on your taskbar, there should be a small NVIDIA logo that says "NVIDIA Settings" when you hover over it. Clicking on it should open NVIDIA Control Panel.

Go to "Manage 3D settings" and switch to the "Program Settings" tab. Wait a few seconds, then click the "Add" button and navigate to where you have the game installed. Click on "NinoKuni_WotWW_Remastered.exe" and click "Open". Set "Antialiasing - FXAA" to "On" then click on the large "Apply" button at the bottom of the window.

If you're suffering from screen tearing (where part of the screen is delayed), scroll down and set "Vertical Sync" to "On". This may cause very slight latency.

Some people have reported that changing the compatibility settings can help.

Navigate to the game's installation folder and right click on "NinoKuni_WotWW_Remastered.exe". In the right-click menu, click "Properties" and switch to the "Compatibility" tab.

Check "Disable Fullscreen Optimisations" and click "Apply"

Click on "Change high DPI settings" and check "Override high DPI scaling behaviour.", then click "OK" and "Apply". You can now close the properties window.

Making sure that your antivirus software's real-time virus scanning is disabled for the game's installation folder can fix some slowdown. The method differs depending on what antivirus software you use.

If all else fails, contact Bandai Namco Support[service-en.bandainamcoent.eu]. They were extremely helpful and fast in helping solve my GPU driver issue.