If you have spare time, the GTK maintainers want people to work on the Vulkan renderer. Benjamin Otte and Georges Stavracas Neto have put in a bit of effort to make the Vulkan renderer better.
GL is only deprecated on Mac from what I understand.
I humbly don't think I am the right guy for that: I use raw x11, and will use raw wayland once the steam client is finally and actually wayland enabled, even though I may do the jump before... because "valve": their "pressure-vessel" is buggy, and I am helping fixing alsa support in SDL3, all that is starting... namely if I code something GFX related that would be more a wayland compositor on drm(dmabufs)/vulkan, probably based on valve one, either in plain and simple C (compiling with tcc, cproc/qbe, simple-cc/qbe), minimal to 0 dependencies without the latest ISO tantrums, or x86_64 assembly (before a port to riscv in the far future).
You shouldn't use raw X11 or raw Wayland unless you're writing a low-level toolkit. If you're working on games, SDL should handle all that stuff for you.
No, really. Those APIs are too low level to be useful for normal applications. Nothing in them is useful for games at all. I don't know why you think it's appropriate to put in these insults either. Cut it out.
It is being retired, it is a massive bloat compared to vulkan (mainly because of the glsl compiler), so it is reasonable to say than building upon it is a mistake.
I see know signs that it is being retired on platforms other than mac. With vulkan you have to bloat your own program's code and introduce complexity. Regardless bloat doesn't matter so I don't know why you are focusing on that.
Unless the article is obsolete itself?