Thanks, it prepared the spawn area and now the server has completely started. Didn't know that some of these commands don't use hyphens. Thank's to everyone for helping.
Ok I forgot the quotation marks at the directory last time. Now the server completely started and the files appeared :). Thank y'all so much for helping me!
I tried it with Java 11 because I got told that I can use Java 8-15. The problem then was that the console didnt even run anything and just closed instantly.
Tried it with Java 11 rn but the window just closed. Then I deleted Java 16 and the same stuff as before happened that the console closes after like 0,5 seconds.
I installed a Forge server, ran the normal .jar file, accepted the EULA, tried to run the forge.jar file but it doesn't give me any folders (like the mods or config) folder. Already looked through the forum here but there weren't any help. I also updated to the newest Java version but it doesn't help.