Preliminary Findings: (Note: Haven’t tried with other plugins deactivated yet)
Successfully, opens app browser and takes me to my wordpress login page.
I can successfully login. I’m taken to my wordpress backend. Mastodon app (Ice Cubes) doesn’t redirect me back into the app from the app browser. Mastodon app continues to say “Sign In”. Never changes.
Sorry, I can just say that I can log in with Ice Cubes on macOS. Could you try temporarily changing your default browser to Safari? Maybe the browser you are using doesn’t support redirecting back to an app.
It doesn’t. After the login works, a redirect back to the app happens. For Ice Cubes that should be icecubesapp://, here you can see a screenshot from my Enable Mastodon Apps settings page:
If that redirect back doesn’t work, it’s more of a sign that in your browser or operating system the “handler” for the “protocol” icecubesapp has not been registered properly. Maybe you are using some tool that blocks it?