To begin with, I want to clarify that I do not consider my point of view to be the only true one and that if you do not follow my advice, then no one will like the game.
Like everyone else, I have my own preferences, I like games with complex internal mechanics most of all and am quite indifferent to linear games. I liked the theme of your game, and therefore I was somewhat discouraged when I found out that there can be only one ending in the game at all.
Nevertheless, I believe that when a person becomes an author, he gets the right to realize his vision as he sees fit.
All I want to do is give you tips that may be able to make the game closer to my tastes, while remaining within the framework of your idea.
For example, the choice only at the end of the game, as if telling the player: "Everything you did before was not important, now is the important moment." While the choices distributed throughout the game, even if they almost do not affect anything until the end, allow you to create at least the illusion that the player is influencing what is happening all the time. In order to achieve this, you don't even need to branch out the plot, it's just that sometimes in conversations you need to make various replicas, which will depend on whether a certain flag is turned on or not, and if you want, one or two completely different scenes, followed by a return to the linear plot. In the case of a large number of endings, it is also possible to make not completely different chains of events there, to create variable sections in a limited number of endings. Also, so that the player does not have to go through the whole game in order to see a different ending, after the endings, you can add a quick replay mode, where the player will be given only all the choices in the game with a brief description of them. So it will be possible to replay the game in a minute and get a new ending, while understanding why it is exactly like this.
