The line between the religious identity and the ethnic identity is unclear to me.

This is deliberate. They benefit from both religious and ethnic protections, picking and choosing based on the situation. They can pose as a religion while advancing their interests as an ethnicity, and vice versa.

As a convert, one might be able to practice the traditions and obey the laws, but wouldn’t they still be lacking something Jewish, like how a tranny putting on makeup and a dress doesn’t make them female?

You are Jewish if you come out of a Jewish vagina. Religious converts are the useful idiots of the Jewish world, permitted to serve Jewish interests and benefit from them only to the extent that your personal prosperity also serves those interests.