Jax is a cautionary tale on the what can happen if you refuse to help yourself or let anyone help you. Goose's trans art for jax symbolises to me that you can be accepted and happy, but only if you allow yourself to be.
TLDR: Queer characters are allowed to be messy and flawed and have trauma.
Last time I was at the store with my parents, we were looking at novelty socks and my mom picked these up and said quietly, "Undertale?"