Was it a Canadian model? That model should technically works on 5G but as it wasn't from Koodo, there's a slim chance it has other issues.

Im assuming it is a canadian model as it is from a canadian walmart, though it doesnt specify. It does say this "Samsung S23 Ultra 5G(vary based on your carrier and location) Dual Sim(international version) 512GB"

https://www.walmart.ca/en/ip/Samsung-Galaxy-S23-Ultra-512GB-Brand-New-Factory-Unlocked-Smartphone/3D0TYG6LNK2A

That is not the Canadian version. We will need the model number to figure out the bands and frequencies. Are you able to ask the seller?

Could not confirm with the seller but I matched the description from another website and it says model number SM-S918B.  Will it still support 5G from koodo? Thanks. 

It should be supported on bands n66 and n78 for the 5G network.