There's no way to switch to the secondary weapon, you just use it by pressing the right mouse button.
Thanks indeed, I was on S. Deck , that's why I didn't figure at first, I'll map a button for sure.
P.D. Yours is avery well crafted engine/game, cherrs to that!
A mash-up or colab between your game and Massif Press-Lancer just makes plenty of sense.
