By installing the latest full installer from this location https://dev.mysql.com/downloads/installer/
by default you should end up with an installation that contains the MySQL 8.0.32 products in the following location: C:\ProgramData\MySQL\MySQL Installer for Windows\Product Cache.
Are you able to see the mysql-8.0.32-winx64.msi in that location? If so, you should be able to upgrade to 8.0.32.
It is expected that 8.0.32 is grayed out when clicking the "Add" button since this option is only intended for new installations.
When clicking the "Upgrade" button you should be redirected to the "Select Products To Upgrade" page where you need to select the products to upgrade from the list of Upgradable Products, in this case "MySQL Server". When doing so, the "Next" button should become enabled.
Do let me know if this helped to resolve the issue. By the way, I believe the "Next" button should be enabled by default without having to first select an Upgradable product. If possible, please raise a bug for this behavior at: https://bugs.mysql.com/
MySQL on Windows Team