I have copy and paste your examples but i don't have any new gas in game that are the lines in the kubejs startup_script

onEvent('infuser_type.registry', event => {

event.create("clay_ball").color(9344921).texture("kubejs:infuser_types/clay.png")

})

onEvent('gas.registry', event => {

 event.create("clay_ball").color(9344921).texture("kubejs:infuser_types/clay.png")

})

Look like something changed in KubJS that broke this addon, I updated KubeJS dependency to latest version and fixed the errors.
The new file on curseforge (MekaJS-1.16.5-1.2.0) should work

just tested with 1.2.0 and I confirm it works, also if you use .texture() be sure to have a texture (.png) file at this location, if you don't, just don't use .texture() and the gas or infuser type will just use the default texture with the color you specified.