Back to Bvckup 2 now and its upcoming Release 75.
With the next release the UI will start adopting a new "progressive refinement" approach for managing advanced and less-frequently used features.
After trying this and that, the design ended up converging to a simple
button at the bottom left corner of the dialog that, when pressed, injects additional settings into the dialog.
This is certainly not something new and revolutionary and it must've been done before, but it does feel a bit more natural compared to a more conventional approach of popping up a separate window with all the advanced extras.
Also, the initial iterations had the More button
between "More..." and "Less..." when clicked, but it looked a tad too busy, hence the current revision of a simple "sticky" background highlight when in the expanded state.