Can’t change Property panel width?

I don’t think that was ever possible. You are welcome to install old versions of WordPress to test or check out the WordPress Core Rollback plugin: https://www.ads-software.com/plugins/core-rollback/

I’m not sure why you want to change the width, it’s fixed but I can suggest a hack. You can use “User JavaScript & CSS” extension where you can set CSS or Javascript rule to set custom width. Just inspect the element and increase the width with csss and set this as a rule on your extension. Hope this makes sense.