Given a movie with ambiguous story, you have multiple options to base your interpretation upon: you have the movie itself, the screenplay if available, what the author said in interviews or books, etc... Now, if we take a video game, you also have additional tools: the source code, the installed file names, unused resources, etc. There are of course a few games that expect the player to check these files but that isn't what I want to focus on.

Would you say that all these files have the same authority as the game itself when it comes to interpretations?

I'd like to take an example with SPOILERS FOR LIFE IS STRANGE 1, as this is the game that sparked this topic for me:

The blue butterfly has a special place in this game, it is what starts the whole journey when Max takes a picture of it and Chloe gets shot. It also shown again in the 'Sacrifice Chloe' ending during that same scene. And later during Chloe's burial that butterfly is shown to land on the coffin in front of Max and fly away. There are some scenes that imply that spirit animals are a thing in the in-game universe. After finishing the game my interpretation was that the blue butterfly was Chloe's spirit animal. Now what a surprise to see in the game wiki that the texture file for that butterfly is named 'Spirit_animal_Chloe' !

Is there any room left for interpretation when the source makes it explicit text? Or can the source be reasonably be pushed aside?

I don't understand what makes the game appealing. It looks like it takes forever to make a level, and why would I want to play levels from random people on the internet?

I like games that you build stuff like KSP but just wondering what the appeal of SMM2 is.

Video game's approach to storytelling usually comprise of mixing gameplay mechanics (gunplay, health system, enemy AI...) and storytelling elements (cutscenes, dialogue trees, environment details...). There are also special systems designed to work both as gameplay challenge as well as narrative carriers (quick time events, the nemesis system in Shadow of War...)

However, there's also a third approach, where traditional gameplay elements when put into appropriate context within the game gain additional narrative significance (the way Thomas was Alone's basic platforming mechanics are personified via narration, or Undertale's combat system being integral to how the story develops...)

Have you ever noticed if a gameplay element also doubled as a storytelling device in the games you played before? If so, what was it and what did it "tell" you?

I personally usually heavily mod my games, due to finding the process of modding itself fun, along with me preferring to spend a LONG time at one run through.

As an example, I'd give minecraft where I usually play so-called expert packs, which are basically taking a lot of mods and making them depend on each other for progression.