As the title states, I am trying to make some advanced settings in the customizer which would be way more organized if I could have some panels nested within other panels.
I found a similar question here: Theme Customizer : how to create multiple-level panel
However the answer provided by OriginalEXE doesn't appear to work anymore.
No, panels are not currently designed to support nesting. This has never been officially supported by core. Any solutions to implement the effect would currently involve hacks. A middle ground can be seen in widgets and nav menus, however, where you can see that controls for nav menu items and widget instances both are expandable to reveal controls. These controls, however, do not appear on separate panes like panels and sections do.
