Valve has confirmed that they are (again) increasing the amount of people that will be invited to purchase a Steam Deck.
Writing on Twitter, the official OnDeck account mentioned:
Hi all, just a quick note that starting with this morning's batch of Steam Deck order invites, we've increased the number of emails we're sending out (again). We're excited to get more of these into your hands! (Order emails are sent out Monday and Thursday mornings PT)
So keep your eyes peeled on your emails around 5-6PM UTC, if you're waiting for that precious invite to come in so you can spend those big bucks on a Steam Deck.
For newer users, be sure to check out my Steam Deck tips article and video to get you started.