roscd can't find newly created packages (Win10/WSL)

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I've already read half the internet, here's what's wrong: Packages created with catkin_create_pkg in a catkin workspace can't be found by roscd, therefore roslaunch etc. don't work either. I already found out that the path to the workspace is missing in the ROS_PACKAGE_PATH, that might be the problem. Here's what I already tried:

• Setting up a new workspace on the same level as the old one. Result: Nothing better.
• manipulating the .bashrc and ROS_PACKAGE_PATH. Result: Spaces in the path to the workspace are deleted, although I used them with escape characters. So the path is incorrect and I get the adequate error.
• Creating a new plain package in the workspace/src, problem as described
• I've sourced the devel/setup.bash a million times, that doesn't fix it.
• Restarting the console permanently (always sourcing setup.bash afterwards)

Also, when trying to launch something (that worked in the exact same workspace before!), I get the error

[] is neither a launch file in package [] nor is [] a launch file name.

My setup is kind of complicated: My workspace is in a OneDrive-synced folder (Win10 file system), which is then mounted using WSL to have a Linux environment for ROS development.