In the latest release of MCreator, any manually made subfolders of src\main\resources\assets\WORKSPACE_NAME\textures (with exception of /blocks, /items, /models) are removed on every build task, making sorting textures that do not fit any of the folders mentioned above impossible (like textures of celestial objects, etc..). Custom subfolders of src\main\resources\assets\WORKSPACE_NAME do not seem to be removed.
Issue comments
MCreator copies resources from own folders into these folders. This is done so once Minecraft versions switching will be possible, MCreator will copy resources in proper folders.
To get own folder into textures folder, add these folder or other files in <workspace dir>/textures/other and they will be copied into src\main\resources\assets\WORKSPACE_NAME\textures
Thank you for your bug report. I will check what can be done to fix this issue and try to fix this in the next update.