Making a datapack containing any feature (i.e. any file in the configured_feature and placed_feature folders) will make that feature disappear from the world, unless the biomes folder is also present in the datapack. Also, it seems that both configured_feature and placed_feature must be present. On 1.17 you could have a datapack containing only some edited file from configured_feature, and it would work correctly.
I attach two datapacks, both contain only unedited files copied from the newest (1.18 pre1) vanilla_worldgen package. One has only some placed_feature configs (trees_*.json), and makes almost all trees disappear. The second has also the files from configured_feature (trees_*.json) and all the biomes, and it works correctly, like vanilla.
Can't confirm or reproduce this in 23w51b. 'pack-working-1.zip' does not work, and will throw a warning when trying to use it:
[media]Said datapack is missing the 'configured features' folder, and adding it back will fix the error. Creating a world with your provided 'pack-without-trees.zip' and my fixed version of 'pack-working-1.zip' both resulted in the same world with expected generation as when generating the world without any packs.
Are you still able to reproduce this issue?