By default games acquired through the Windows Store, including those on Game Pass for PC, install to unchangeable read-only directories, making them impossible to mod. However, some games have a toggle to alter this, meaning the Game Pass versions of FTL, State of Decay 2, and a handful of others actually can be modded. And so can Skyrim Special Edition, one of 13 Bethesda games recently added to Game Pass (opens in new tab), and a game that's improved significantly by mods.
However, it's not all good news. The Game Pass edition of Skyrim Special Edition has a different executable to the Steam release, and is incompatible with the Skyrim Script Extender (SKSE). Without SKSE, many of the most popular and ambitious mods won't work. According to the SKSE webpage (opens in new tab), it may stay that way. "SKSE cannot support any potential Windows Store release of Skyrim", it says. "Windows Store applications are locked down similarly to consoles and do not allow the APIs necessary for script extenders to work."
So no SkyUI (opens in new tab) or Legacy of the Dragonborn (opens in new tab) then. There are still great mods out there that don't require SKSE, however, like those collected at Bethesda.net (opens in new tab). If you've got Skyrim through Game Pass, you'll still be able to use Alternate Start—Live Another Life (opens in new tab), A Quality World Map (opens in new tab), Inigo (opens in new tab), and The Forgotten City (opens in new tab). Here's our list of the best Skyrim Special Edition mods (opens in new tab) to help you find more, or see what you're missing.