Regarding Joplin: I don’t know what you mean by callouts, but it does have a plug-in system. Perhaps there is one containing what you need?

If not, and it’s not beyond your skill set, you could build it yourself.

Did you read the article? Simple text and PDF readers are in the cross hairs. Apps that aren’t “engaging” are in the cross hairs.

I expect developers of perfectly fine apps will have to manually vet those apps with Google.