check your documents/humankind/community folder. There may be more than one version of your mod there and the game is loading the older one. If thats the case, you need to delete the older folders and keep only the most updated one. 

Thanks for the reply! Sorry for taking so long, I was gone for a while. At some point the mods just appeared and it worked out. However, today HK updated itself and now my mod is gone from the ingame mod section. I went back to the Unity project and built the mod again, but this does not help. Any idea how I make it reappear? Do I need to open another project and do all changes again manually?

Thank you! I found the button, updated the programme, reimported the project, built the mod once more, and restarted the game and now it finally finds the mod. Thank you once more!