The only thing proprietary about the main distribution of be code, that i can tell, is the configuration. I'm not aware of any differing functionality or limitations on the open source code. MS states that their distro is the same code but with their own configuration in the product.json file.

It's not open limitations but about extra Microsoft spyware included and making you agree with Microsoft Privacy Terms https://code.visualstudio.com/License/

"The software may collect information about you and your use of the software, and send that to Microsoft. Microsoft may use this information to provide services and improve our products and services. You may opt-out of many of these scenarios, but not all, as described in the product documentation."