Experience Cloud Users are all managed within the central Admin Console. If you are an Admin of your org, these steps shouldd work:
1. Login to marketing.adobe.com and make sure you have the correct Organization selected if you belong to multiple.
2. Click the 3x3 square (product selector) from the top right corner.
3. Choose "Adminstration" from the right side
4. Launch the "Admin Console" where you as an Admin can control all users and permissions for your Organization.
5. Scroll down and select the "Launch, by Adobe" card - not the "Launch API" one.
6. Choose "Product Profiles" tab
7. Either create a new one or select one that is already existing
8. If you do not see your user in the group, click "Add User" and add yourself
9. Then click the "Permissions" tab
10. Expand the "Rights" section
11. On the left are all of the different permissions that can be added to this group you are editing. The "Manage Properties" right must be granted to this group you belong to in order to create new Properties.
12. Add additional rights (all if you wish) as you see fit to this group and click save.
13. Go back to the Launch product and your user should now see the button to create a Property.