After I turn on the Sync plugin across my three devices and setup the third party plugin sync,I cannot turn on my third party plugin any longer .
My 3 devices are Window PC with Win10, iPad and a Android Phone with Android 11. And I turned on the switch to enable third-party plugins in the sync plugin on all three devices.
On an Android phone, you won’t be able to turn on plugins that aren’t compatible with the mobile app. Probably the same with the iPad. Could this be your issue?