Like the previous game, God of War Ragnarök likes to have you revisit each area multiple times as part of the story, or with new tools that open up new possibilities. It is therefore difficult to judge if you are facing a devious enigma, or if the path will open up naturally a little later. This is the case, for example, when you visit the heights of Svartalfheim for the first time, and you come across the closed doors of the Forge.
Can the Forge door be opened the first time?
The short, spoiler-free answer is: no, not on your first visit to the region , during Chapter 2: In Search of Tyr. As you might have suspected, this is an area you will come back to later. You can continue on your way and take the second cart, after clearing the way. Take the time to thoroughly search the area, since you won't be able to return to it for a while. The Heart Painted on the Rocks is tied to the Across the Realms service, but you don't have it yet, and you can't do anything with it either. Still in the same vein, the Chest of the Norns in the area cannot be opened without a tool which is acquired much later. Finally, a local Odin's Raven is inside the Forge, you can't reach it right now.
How to open the Forge door?
For a more detailed answer, with some spoilers, we will have to go much further in the story, until Chapter 9: Forging Destiny. During the previous chapter, Kratos learns that he needs a new weapon. He must therefore go to the Forge with Brok the Dwarf. The problem is that the area around the Forge has become inaccessible, due to your various cart accidents on the way.
From Sindri's house, Brok will create access to the fast travel door for you, which will teleport you to the bottom of a large storage cave full of monsters. You will eventually come out, not far from the entrance to the forge. A few fights ensue with Brok, and once there, he will simply go to the other side and open the door for you . Knees being Kratos' weak points, jumping over them wasn't an option, unfortunately.
At least your patience will be rewarded, since you will receive the fantastic Lance Draupnir, which will allow you to access many additional areas and treasures, everywhere in the game. It is also quite fun to use, especially from a distance .