It was my mistake. I tried the solution before, but made a syntax error:

• in .swipeActions:

  Button { editLesson(lesson: lesson) } label: { Label("Edit", systemImage: "pencil") }

• the called function:

  func editLesson(lesson: Lesson) { forEdit = lesson }

• the sheet:

  .sheet(item: $forEdit) { editLesson in NavigationStack { EditLesson(lesson: editLesson).environmentObject(realmService) } }

Now it works without any problems. I forgot editLesson in inside the sheet syntax. Thank you for your comment.