Here's you can add a new portfolio page.
1. Go to https://www.coingecko.com/en/portfolio and click on the dropdown in the top left corner, then click on "Create Portfolio"
2. Insert a name for your new portfolio. Once you are done, click "Create"
3. Now, whenever you add a new coin, you will have the option of adding it to the portfolio of your choice. Alternatively, you could also click on "Add to a new portfolio" in this dropdown, which is another quick way to create a new portfolio.
Note: Creating new portfolios is only available on desktop at the moment. On mobile, you can still have the option to choose which portfolio you want to add the coin into once the portfolios have been created on desktop.