It depends on what kind of game we are talking about. If you are referring to games that have only text without a visual as such (unless this games, for example, breaks the fourth wall, but visualization is also necessary for this), then I would rather skip them. After all, this is more of a book than a game, even with the choice itself. I would advise you to pay attention to visual novels. An ageless genre. And there are an incredible number of possibilities for realization and immersion in the plot now
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After all, this is more of a book than a game
If it is a linear "game", yes. Same goes for kinetic visual novels.
But even regular books can feature illustrations. In the extreme variant you have a graphic novel comic book.
There is even those chose your own adventure books. Some with dice rolls and other rules https://itch.io/physical-games/tag-solo-rpg ;-)
In general, there are a lot of volunteers now - they train their skills, or help as a gesture of goodwill. You can temporarily use AI-generated thumbnails (as I did, while the artist draws the content I need). So, if it's a prototype, I don't see anything wrong with it. Or just search on itch.io - there are many artists here. That's how I found a translator for my project, and she just asked me to include her in the credits