I'm not a fan of "portal" since that implies that there isn't much difference in which one you pick. For example, it doesn't really matter which Matrix server I create my account on, I'll have access to the same content.

A Lemmy instance is quite important to the experience since admins can hide certain types of content (word filters, instance blocking, etc), have different rules, etc.

When I think of "portal," I think of something like an ISP, web browser, messaging client, etc. They all connect to the same place, and outside of a few cosmetic differences, they essentially do the same thing.