The recipe for glass is unavailable when using AAI, Crushing Industry, K2SO, and K2SO Tweaks together.
Examining the "Sand Processing" entry in the tech tree shows that it doesn't unlock anything. Neither does the "Glass Processing" entry.
This is NOT caused by K2SO Tweaks, but it seems like a good place to fix it.

elevated-rails 2.0.69
quality 2.0.69
space-age 2.0.69
aai-industry 0.6.13
crushing-industry 0.4.13
fsdl 0.2.2
flib 0.16.3
Krastorio2-spaced-out 1.4.26
Krastorio2Assets 2.0.3
Krastorio2Inserters 1.1.6
Krastorio2MenuSimulations 2.0.2
multispoil 2.1.2
nulls-k2so-tweaks 1.8.1
PlanetsLib 1.13.6

Looks like this is still the case, has anyone found and/or made a fix?

Going back to an older version of the crushing-industry.lua file (Reverting the oct 4 commit regarding the k2 glass recipe) fixed the issue.

Edit: Not sure if it's because it was changed in an ongoing savefile or if it's something else, but the recipe is now showing up as
Uknown Key: "recipe-name.kr-glass"

Thanks Asriel, I reverted the change too, I can now progress.

@NullCascade - glass research doesn't unlock glass recipe in smelters when you start as of 1.12.0 - 2026/01/01

Attempted fix in 1.13. I don't play with AAI Industries in my K2SO run, so I can't promise it is fully functional. But at least I see recipes available in the early tech tree in a new game.

In my environment using AAI, K2SO, and K2SO Tweaks, this issue started occurring after updating to 1.13.0 (now I use 1.12.0)
It seems that the recent fix may not be working correctly...

Give 1.13.1 a try. Though again I do not use AAI Industry and the goal of this mod is not to make K2SO compatible with every mod. I'm just uploading fixes and additions I made for my own K2SO+too-many-other-mods play through in case anyone else wanted them.