Folder icons view-Macbook

The Open/Save dialogs are basically limited Finder windows served up by MacOS.

Editing the plist is a way to increase dialog thumbnails, but not sure I'd want anyone new to the Mac doing this quite yet:

You can use the Spacebar on your Mac to get an expanded view. My trick is to use List View, press the  spacebar on a selected image to look at it. Spacebar will close the expanded image, but keep it open and use the cursor keys to scroll through your images in expanded or quicklook mode.

Bridge 2022 is Adobe's File Manager program free for downloading from your Creative Cloud Desktop. You can adjust your thumbnail sizes there and open your files in Photoshop.

If you want to you can try the plist adjustment, but I've only used it on Catalina--MacOS 10.15.7  You have to purchase the Plist Editor from the app store.

The issue is the thumbnail size is fixed in the file open dialogs, however, you can change the size as explained here by gener7.

https://community.adobe.com/t5/photoshop-ecosystem-discussions/increasing-size-of-thumbnails-for-mac/m-p/12123630

Apple sells Retina displays, which are normally scaled down to usable size. I have a 15" MacBook Pro and a 21" 4K iMac, and both are scaled to 50% of native resolution.

https://support.apple.com/en-us/HT202471

If my above suggestion doesn't help, could you please post a screen capture to show exactly what you are trying to scale.

The Preferences can be found in the Photoshop menu on a Mac and the Edit menu on Windows. Within the Interface section is the ability to change the UI Font Size and scale the UI. Don't forget to restart Photoshop. Does this help?