Yes, as this is the way the BLO devs figured would be best to combat cheaters, RMT, and account sharing.
In the
Steam Account Linking post made by moonlight.exe (Community Manager)
Unfortunately, the restrictions mean that it will not be possible to play Epic Games Store or GOG versions of the game.
If you've been using a version of the game from one of these platforms, you can purchase the game version right now for 50% off during Steam's summer sale.
So, until they add a way to link Xbox PC (PC Gamepass), GOG, and Epic accounts, the only way to play BLO is via the Steam release.
As far as I know, Xbox PC version doesn't allow mods, or most modders don't bother with making the mods compatible with Gamepass.
Mainly because of how horrible modding the game is. (Having to fix mods with most minor updates (bug fixes for the most part). I could be wrong though if this is part of the reason why mods most mods aren't accessible on Xbox PC Gamepass, but, it is the reason why so many mods just became abandoned.