Yeah, that's what I thought.
A chair with wheels isn't too hard to see at any point in human history, whether it's moved by arm-power, pulled by dogs, or has a magical enchantment. Especially in a fantasy version of human history with monsters and magic in the mix. A quick internet search reveals that wheelchairs actually go back to the 5th century BCE, and, get this . . . as depicted on a Greek vase!!! It's unclear if self-propelled chairs existed before 1655, but wheeled chairs go way back!
I've actually been wanting to run a Greek-themed campaign for quite some time, based on the Odyssey of the Dragonlords campaign, the Mysteries of Theros campaign, and a few other "Greece 5E" sources. These settings are all high-fantasy, but I can see certain D&D-isms or historical anachronisms that wouldn't seem to fit the theme. If none of my players, like yours, are disabled, then I wouldn't even spend brain power on wheelchairs in my ancient fantasy Greece.
But if one of them were, or a disabled gamer joined us later, and asked for their character to be wheelchair bound . . . I would totally accommodate that, no question. My precious campaign theme is not as important as making my players feel included and seen. And it wouldn't be hard to do at all, and stay within theme. If my other players balked at the idea . . . they could leave or stay, I like to play with people who also prioritize inclusivity and treating others well.
Chiron, the reclusive centaur philosopher and inventor is friends with the PC's parents and saw a need he could fill with invention . . . so he invented something never before seen, a chair with wheels the PC can move with their own arm power! Over the PC's childhood, Chiron went through many iterations until arriving at the current design . . . and has more ideas should the PCs swing by in the future!