I've recently discovered, that GitHub is no longer maintaining the Atom Editor. The packages can no longer be installed, as this service has already been shut down.
I love the Atom Editor and I do not want to use Visual Studio Code, like suggested by GitHub (i.e. Microsoft).
Is there any reasonable and functioning fork, that will continue to work on this editor?
As no one posted an answer so far, I will post my temporary solution.
I discovered a fork named Pulsar. This editor seems to be in an early beta stage, but it's able to install packages, although some of them still have some issues, like PlatformIO, which kind of works. But it's better than nothing.
Pulsar Editor can be downloaded at https://pulsar-edit.dev.
This question/answer is not an advertisement by any means. If someone knows a better functioning fork of the Atom Editor, please post an answer.