Well time for more worldbuilding brainstorming. I've been doodling what early hexapods must have looked like to get an idea of how evolution worked.
Since my headworld is essentially an alternate Earth, it has gone through a similar geological timescale and extinction events. For most of it, hexapods were limited to small animals, given how maintaining an extra set of limbs on land isn't as taxing on the body and locomotion at a smaller scale.
So for the most part, hexapods were just crawlers and burrowers at the nooks and crannies of the food chain, while the world was dominated by reptiles and dinosaurs that either had long lost their extra limbs or kept vestigial ones.
By the time the KPG extinction event happened, there were already little hexapodal mammals lurking around, many of which were well specialized for an arboreal lifestyle and had their extra limbs modified to climb. With the extinction of dinosaurs and a much more efficient metabolism, these mammals were able to evolve into much bigger sizes without losing the third limb set as it served such an specific function.
And this lineage of climbers would set the pathway for the evolution of dragons.
In the present day, pretty much all extant amphibians have maintained the third limb set to some extent, often using them to aid in swimming and digging after food. Some may even use them for mating and threat displays.
And here are some sketches for little hexapod critters, one being a gecko-like reptile and the other being a semi-arboreal protomammal.
I also played with the look of a larger reptile with vestigial limbs. It's easy to imagine it angrily flapping them for some sort of display lol.
And as a bonus, here's a dragon wannabe :D