The steeled boots I wore, matching the full armored suit, was making me suffocating, despite no being the first time wearing them.
The correct tense is "suffocated" based on how you constructed your sentence, and no should be "not" (like I said above, forgetting the t is not critical; it's just a mistype, so I overlooked these). However, the syntax/structure of this is still off. I noticed you like to use a lot of commas, and while the large majority of them were correctly placed (which is quite rare as I more often come across comma splices or lack of any where there should be), I believe it hinders your sentences from the most intuitive syntax. A better way to construct this sentence is "The steeled boots I wore, which matched my full armored suit, was suffocating me despite it not being my first time wearing them."
Another instance follows right after this...
At this day, at this moment, their cheer for me nearly got me puked, not knowing how, I found myself walking to the end of the balcony, overseeing a sea of people stretched as long as my eyesight could go.
Firstly, this sentence is too long; it's actually a run-on and should be split after "puked." However, due to how it was constructed, it cannot simply be split exactly here and be correct. If going along with this single sentence form, then the correct tenses are puked and stretching instead. But again, the structure is not intuitive even with these tense corrections. "Got" should almost never be used in most cases as it's like a weed in sentences. It hinders usage of the proper terms or is a filler word in itself. Thus, the best construction and word choice is "At this day, at this moment, their cheer for me nearly made me puke. Not knowing how, I found myself walking to the end of the balcony, overseeing a sea of people stretching as far as my eyesight could go." Now this could further be revised even better, but those are the most subtle of changes to make it grammatically correct. Another option is to change the first sentence to "At this day, at this moment, their cheers nearly made me puke." And you can do this because in the previous sentence, you already mentioned that people cheered for the prince as soon as they saw him.
Outside of the technical aspects of writing, I'll dip a little into what I thought about your storytelling. You are able to navigate through a game world very well with various quests, dungeons, and other details. This is essential for LitRPG, and whether or not a reader knows video games well, this was generally quite clear.
You also have great original ideas such the NPC into Player one. Having a NPC from an abandoned game join a competing game as a player instead is fresh! However, I don't think you capitalized on this idea as much as you could have nor did you explain exactly how this is possible. While you don't have to be technical and logical about how a "fictional" NPC could become a player controlled usually by a live human as this is fantasy after all, you still need some logical rationale. Otherwise, as it is right now, the NPC could be replaced by any human player and it would literally not affect the story in any major way.
Some supportive details to this main idea of NPC into a Player could be that the NPC became an AI during the peak of the game it was in; thus, it essentially hijacked into another game. And to make it more interesting, if he dies in the game world, he dies "for real" since he's not a real person. This would give the story another layer of tension and more thoroughly capitalize and emphasize he's a NPC. And as the MC likes engaging with details of the game world that the system even tells him not to be so shameless (like with the caravan), maybe as a NPC, it can interact with more of the game world more than any human player could. In essence, no place is off limits as normal players have walls or boundaries of where they can go. Furthermore, making a NPC able to interact with other NPCs outside of usual player constraints could also be another "hack" he as a NPC could do. And lastly, more of his lore in his past game in connection to the competing one would be a nice tie.
In short, you have solid story ideas and writing which could further be improved. But overall, I think you're doing great with a lot more potential in store.