Do mods make you ineligible for Steam achievements?
Generally not!
If the mods do not change content, mechanics or events which triggers the achievement, they are no problem.
Steam doesn't disable achievements,developers can disable achievements if you install mods or something else in game. Some games check for mods like Skyrim SE and disable achievements until you disable or delete the mods. In many single player games, developers don't disable achievements because you don't get any advantage in game if you complete any achievements.