You can try to go straight to north, south, west, and east. Unlike Minecraft Java Edition, there isn’t a “/locatebiome” command in Minecraft Bedrock. So you pretty much need to find it yourself. But Desert isn’t a rare biome though, I hope you find it.

And about the Nether Fortress, this Website doesn’t provide you with the location of the Nether Fortress. Sorry. Partly because it’s hard to give the exact location. I mean, what’s the point if you always need coordinates to visits some areas or structures?

Thank You.