Create a single product category to list all products
In WHMCS version 8.0.4 with the six stock template Browse All is redirecting to first product group where as it should list all products in page index.php?rp=-store.
I have checked and this is the way the stock template is suppose to behave. When you navigate to Store > Browse All it will only show the first product group. Unfortunately, the functionality you're looking for here is not something that is currently offered by WHMCS stock six template.
I request all WHMCS user to vote for this enhancement.