The current proxy panel is mixing functions which will work on active strip and selected strips, and this makes the panel(s) more confusing. And also leave all elements active while Custom File should make them inactive.
The main idea behind the design suggestion is to move active strip related proxy functions into the Strip tab and let the Proxies for Selected Strips stay in the Proxies & Cache tab.
After - Active Strip:
After - Active Strip - Custom File toggle:
After - Selected Strips:
I realized that using Custom File needs to disable except the Resolutions, because the selected resolution will only enable the Custom file, when Viewed in that selected Resolution. This is a huge part of what imo causes a lot of confusion in this panel - that buttons are used differently depending on what else is selected(same thing with the Rebuild Proxy in the old layout).
Make Build Proxy button inactive when no resolutions are selected.
In order to keep consistency for functions related to the active strip are in the Strip tab, the Strip Cache functions has been moved here too.
Several Effect panels where below the Adjust panel, ex. Scene, Text, Multicam Strips they are now above the Adjust panel, like the more general Effect strips.
The proxy building entry in the Strip Menu has been renamed to "Rebuild Selected Strips Proxies" so it is in consistency with the panel.