The first version of the custom feeds exploration view, using a secondary sidebar, seems too unbalanced:

We can move the main area to the left recovering some space from the sidebar, but the effect remains the same, especially on large screens:

The problem with the current solution is that feeds are not visible at all, and this is a shame since they are a powerful feature.

We have at least two more options:

1. Let the user navigate a sub-menu inside the same sidebar, collapsing the first one in a narrow column:

The main problem of this solution is that this specific view should be the initial one, so the user would start with the main menu collapsed, and this is a poor UI/UX. To solve that, we could put on the main menu two items: "Main feed" and "Custom feeds".

2. An alternative solution is to move the secondary nav to the right, with the same width or slightly narrower than the first, centering the main block:

The main problem of this solution is that the central block would move to the right when changing section (e.g. notification, messages, etc), giving an annoying "bouncing" feeling; the solution could be to always keep a secondary "ghost" column, to be used possibly in other contexts, for example to display the note details (liked and zapped by, nevent, etc).