If you want a game that can last 1–3 months, Minecraft with mods is honestly a really good one. Once you start installing big modpacks there’s so much stuff to do that it can easily eat up months. Skyrim with mods is also like that — people still play it for years because the modding community keeps adding new content.
Stardew Valley is another one that can quietly take a lot of your time. You just keep playing day after day building your farm and suddenly you’ve spent dozens of hours. Terraria is also fun if you like progression and boss fights.