In many ways, this discussion is the same as the tire size discussion. If you come from road cycling then you'll expect a bike to have two chainrings in the front. If you come from mountain biking then there's more variation but the industry has largely switched to a single chainring. Choosing the best gravel groupset really depends on the riding you plan on doing.
A single chainring up front makes a bike easier to handle over more technical surfaces. Front chainrings need some forethought when switching. It's also best not to fully cross the chain between the front and the back of the bike. That means a bike with two chainrings will sometimes end up getting caught in the wrong gear if the ride suddenly gets steep and rough. You can't always look down and assess what gear the bike is in and even if you can, changing the front chainring might upset the balance of the bike. Needing to only worry about the rear cassette means you keep your eyes on the road, or trail, and change gears as needed.
The downside of a single chainring is that you've got fewer gears to choose from. Fewer gears but a similar range mean the jumps between gears are bigger. High-end setups solve this problem by adding gears in the rear cassette. At the price point though you aren't going to see 12 or 13 gears in the back. That means, just like with the tire choice you'll have to decide what you think your gravel bike will be doing more of. Off-road use makes a single chainring, or 1x, a better choice. Mixed surface riding makes a double chainring, or 2x, a better choice.
Unlike with wheel size, this choice is slightly more permanent. Many bike frames have provisions for later adding a front derailleur but it's not a small change. You'll need an entire new groupset and it's a somewhat major undertaking. It's not impossible but it's best not to count on changing the groupset anytime soon. The good news is that you can use either 1x or 2x for any riding you want to take on despite the advantages that they give you for different types of riding.