Private sector can develop it. Developing a 5th gen fighter will mean competing with well established F-35s. These projects are still in the planning phase so becoming 6th gen is quite likely. They don't really need another 5th gen. It has little to do with relying on USA for defense because they can defend themselves more than easily enough from Russia, instead it is Russia who is now far behind and feels the pressure. Some are probably eyeing Russia's abundance of natural resources and land with certain plans for the future. Europe has F-35s now ergo no need to hurt the budget with another expensive overlap in capabilities. But they still want to improve these industries so exploring 6th gen is well within Europe's interest especially now they have time on their side. USAF is invested into 6th gen PCA and PLAAF has programs in place as well. At the moment nobody has come out with well defined abilities of 6th gen and most players are probably going independent routes.