I’m also having this issue. There is no Steam class, no gd files apart from godotsteam_plugin.gd and updating.gd. I’ve downloaded the plugin from the asset store and the repo’s releases on separate occasions…
But basically from my understanding, the steam API belonging to the godot installation doesn’t really update while the addon’s does, so we just need to replace the steam_api64.dll located at C:\Program Files (x86)\Steam\steamapps\common\Godot Engine with the steam_api64.dll located in res://addons/godotsteam/win64/