I’m in the same boat. Can’t play Burning Shores because I got the game for my PS4.
It was a dual release because Forbidden West was developed for PS4, not the PS5. Essentially, the PS5 version is a port with some upgrades to take advantage of the hardware.
The DLC was developed post-release, and with the PS5 out and ready, Guerilla made the choice to take advantage and do things in the DLC which the PS4 couldn’t handle. Hence it wasn’t possible to make the DLC a dual release same as the base game.
But the PC version will be a port of Complete Edition, not the original base game. The PC port was announced in the Complete Edition release trailer.
Meaning the DLC doesn’t need to be “released” for PC. Like with Frozen Wilds and the PC version of Zero Dawn, Burning Shores will simply be part of the PC version of Forbidden West.