[2023] (SOLVED) Galactic Paragons dlc bought on steam, but it doesn't show up in paradox launcher

The Rogue Admiral said: Its a bit odd that the old launcher is automatically downloaded after installing the game through steam, when its defunct.

It is not defunct. It has two operational modes; standalone non-Steam compatible, and Steam-compatible when triggered by Steam. You are now using the second mode, as the first mode is no longer supported by this game.