Yippee, as our little friends say.
Now I have found the right way and have already loaded various level packs.
Thank you again.

Hello kaywhyn,
first of all: Thank you very much for your help.

My folder looks different.

I'm at a loss. I did everything like that.

    https://www.dropbox.com/s/fkrqzojlfrwnen7/NepsterLems.zip?dl=1
and
  NeolemmixPlayer unpacked into a folder.

In the level select there are only levels from the Neolemmix player.
However, once it worked with Lemmings Halloween 2023.

Sorry, maybe I'm too stupid...

Sorry for my bad English. I'm from Germany and would love to play Lemming again because I'm a big fan of the game. Unfortunately, I'm not good at computers.
For example, Nepster, LemRunner or Blizzard of Lemm, which I downloaded as a ZIP file, do not open with the NeoLemmix_V12.12.5(1) player. Only the Neoplayer games themselves. What am I doing wrong? How to do it correctly?
Please don't laugh at my ignorance.