No surprise to see the Steam store crash as the summer sale kicked off. The sale runs from June 25, 2019 to July 9, 2019 this year.
Typically many of the games on my wishlist were on sale but I prefer 75% or more off mostly as I already own hundreds of games.
Steam runs their own server suggesting that the traffic was more than the machine could cope with.
Obviously Valve has underestimated the demand this year again. The servers there crashed last year too.
Azure and other cloud services have a lot of experience with load management and busy web servers like Facebook and Twitter manage fine so Valve may need to look at some of the heavyweights for ideas on how to prevent the store from crashing all the time.
It seems that all through the summer sale the Steam client kept throwing HTTP 500 errors. Clearly Valve needs to hire somebody like me with some experience at running a high traffic web site.