how to enable new acrobat ?

I had a similar issue, and have been struggling to know why I don't see "Enable new Acrobat" in my Adobe Acrobat Pro updated version on Mac, I even had the chance to speak with three of the Acrobat development team without getting a solution!

What I did just now and had the "Enable new Acrobat" option visible to me finally…

1. I Uninstalled Acrobat Pro
2. Uninstalled Adobe Reader
3. Used the Acrobat Cleaner Tool to clear the full registry
4. Reinstall Acrobat Pro

Although I listed three steps above, I strongly doubt the culprit is Adobe Reader. So for those of you who had this same problem. Try removing Adobe Reader from your machines - if you have it installed alongside Acrobat Pro. Try the other two steps if this step alone doesn't solve it.

It depends on your location (US & UK) and the language (ENG) of your system.

To enable the new version of Adobe Acrobat, you can follow these general steps:Ensure that you have the latest version of Adobe Acrobat installed on your device. You can download and install the latest version from the official Adobe website.Once the installation is complete, launch Adobe Acrobat on your computer.If you are upgrading from an older version of Acrobat, which the new version may automatically detect and import your existing settings and preferences. In such cases, you can proceed with the default settings.If you are using Adobe Acrobat for the first time or if your previous settings were not imported, you may be prompted to set up your preferences. Follow the on-screen instructions to configure your desired settings such as language, default document settings, and other preferences.

Read the note on this page:

https://helpx.adobe.com/acrobat/using/new-acrobat-experience.html 

It is possible when you have a installation of Acrobat with the new UI.