What parts are compatible with the SRAM RED eTap AXS 36T Max rear derailleur? Can I use a SRAM RED 36T Max rear derailleur with my 11-speed SRAM RED eTap system?

The SRAM RED eTap AXS 36T Max rear derailleur is only compatible with SRAM AXS systems: they will communicate with AXS front derailleurs, drop bar shift levers, BlipBoxes, and controllers only. The SRAM RED eTap AXS derailleurs are not backwards compatible with SRAM RED eTap 11-speed components as they are not able to communicate with each other.