Every biome has a surface layer of normal grass blocks with no variation when generated as a Single Biome world. This is most apparent with biomes that normally don't have a surface layer of grass, (including desert and badlands biomes, biomes with lush grass, biomes with overgrown stone, and biomes with a dacite layer) but almost every biome is affected to some extent.
Notable instances and possible exceptions:

• Swamp biomes (Bayou, Cypress Swamplands, Pale Bog, and White Mangrove Marshes) still generate pools of water. Mud generates beneath some grass blocks and water, and Pale Moss still generates in the Pale Bog (but not Pale Mud)
• Basalt Barrera columns generate over top of the grass, like the Basalt Deltas biome does in vanilla
• Crag Gardens seems to work fine b
• Because the Dacite Shore now has a grassy surface, foxes, wolves, and other animals spawn there.
• Dead Sea generates as described, but Lush Stacks generate the same terrain that Lush Caves biomes do in Single Biome worlds.
• For sandy biomes, such as the Mojave Desert, proper vegetation may still generate on sand that generates as part of a shoreline. This sand will always be regular vanilla sand, though.
• Eroded terrain in the Shattered Glacier is made of normal grass/dirt/stone instead of black ice.

Not sure if this is a problem with this mod or with Terrablender.
I'm using the latest version for NeoForge 1.21.4

This is a known issue with terrablender, please report to them