The simplest modification to your routine is

sub myopen {
   my ($file, $mode, $locktype) = @_;
  
   local *FH; ## Ensure that we get a new GLOB each time

   #open the file...for the sake of brevity
   #I'll not include the mode logic here
   if (open FH, "$file"){
      print "Opened $file successfully.\n";
      #lock the file
      #do whatever else needs to be done
      return *FH;
   } else {
      warn "Can't open: $!\n";
   }
}
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