To reproduce:

https://lesscss.org/less-preview/#eyJjb2RlIjoiLm1haW57ICBcbiAgQGxheWVye1xuICAgICY6OmJlZm9yZXtcbiAgICAgIGNvbG9yOiNmMDA7XG4gICAgfVxuICB9XG4gIEBtZWRpYSBzY3JlZW57XG4gICAgJjo6YmVmb3Jle1xuICAgICAgY29sb3I6IzBmMDtcbiAgICB9XG4gIH1cbiAgQGNvbnRhaW5lciAod2lkdGg+NDAwcHgpe1xuICAgICY6OmJlZm9yZXtcbiAgICAgIGNvbG9yOiMwMGY7XG4gICAgfVxuICB9XG59IiwiYWN0aXZlVmVyc2lvbiI6IjQuMi4wIiwibWF0aCI6InBhcmVucy1kaXZpc2lvbiIsInN0cmljdFVuaXRzIjpmYWxzZX0=

.main{  
  @layer{
    &::before{
      color:#f00;
    }
  }
}

Current behavior:
Nesting selector & lost in @layer.
But other @ rules works well, such as @media, @container etc.

@layer {
  ::before {
    color: #f00;
  }
}

Expected behavior:
Nesting selector & resolved as its scope selector.

@layer {
  .main::before {
    color: #f00;
  }
}

Environment information:

• less version: 4.2.0