Java 1.15.2 and is that also possible for an Aternos server? If you don't know what a dropper map is, you can also say where you can generally install maps.
You insert a map at Welten (the download link) that is in the menu on the side
What are you talking about?
Which link and which menu?!
You can download the worlds online and then install them either on your client or on any server.
If you only want to play single player, you have to insert the map in your Saves folder at "Roaming \ .minecraft \ saves".
If you want to install it on a server, simply paste the world into the server folder and name it "world".