Can't preview my PHP project in browser

For details on defining your local testing server in DW, see this reply from a few days ago. You need a local server to parse PHP code.

https://community.adobe.com/t5/dreamweaver-discussions/re-help-setting-up-php-environment-on-xampp-branched-from-2010-topic/m-p/12747954#M216447

Which testing server do you have  -- Wamp, Xampp or Mamp?

Did you launch your local testing server and are all PHP & Apache processes running?

My local site folder resides in my testing server's default web directory (www on Wamp, htdocs on Xampp & Mamp).

Real-Time preview does not play nice with my local testing server.  So I disabled it in Preferences as shown below.

What workflow are you using to connect to your database/localhost? If you are deploying the inbuilt server behaviours from an old version of Dreamweaver or have re-instated them into Dreamwear to connect using a version of php above 5.6 then the server  behaviours  will not work, they are out of date beyond php version 5.6.

Does that sound like something you are trying to do?