I asked ChatGPT the same. Here is its answer:

On ResearchGate, it is generally possible to make improvements and additions to your manuscript after it has been assigned a DOI. However, the specifics of whether you can keep the same DOI and article title depend on several factors, including ResearchGate's policies and the nature of the changes you intend to make.

Here are some key points to consider:

To update your manuscript on ResearchGate:

• Go to your ResearchGate profile and find the manuscript you want to update.
• Select the option to upload a new version.
• Follow the prompts to upload your revised manuscript.

It's a good idea to check ResearchGate's specific guidelines or contact their support team for detailed instructions on how to proceed with your specific updates while maintaining the same DOI.