Change Shimano GRX 1x to 2x
It depends. For most gravel bikes it will be an easy, yet expensive, swap. A couple of gravel bikes frames are built in a way that makes shipping a front derailleur as good as impossible. There may not be enough room for the chain stays to clear a second chain ring. What is more, some frames lack mounting positions and the shape or material of the seat tube does not allow clamping. A minor obstacle might be cable routing.
Many gravel bikes come in 1x and 2x configurations. Only the group is different while the frame is identical. Migrating on these bikes from 1x to 2x is easy to do.
The costs involved are substantial though. You will need to replace crank-set, brifters, rear derailleur, chain, bar tape.
Unless you use SRAM's wireless group you also need to rout a cable. As before, gravel bikes that come in a 2x configuration make this easy. Bear in mind though, for internal cable routing you might have to remove the bottom bracket. Cable routing can be substantial and frustrating work, and may be expensive in a shop.
With so many components to replace, a good way to estimate component costs is to look at the price of a group set. It is typically at about 1/3 to 1/2 of the complete bike's price. Together with small parts and finishing kit you can expect the cost of modification to exceed the value of the bike after a year of riding.