There are several ways.
If you have already created a portfolio, you can click on the respective portfolio and press "Edit" at the top right.
You can then select all investment instruments by clicking on the "Add instruments" button.
If you open a new portfolio via the "+" symbol, click on "Add theme fund"
and select at least one fund and confirm it, then you can click on "Add instruments" again and you will now also see all investment instruments.