bought it on Thursday and I still have no notification of purchase or download itch.io, I also find that it is available in Syeam and cheaper than I have paid, very well for this sales system :(
It is the same price on Steam and itch.io.
The download links, and claim steam key buttons should be visible on the itch store page for the game if you've purchased it.
If you're having problems using the itch website please contact itch support.