Surprised a year after lions created the simple solution with string, the industry still sells elaborate systems of PTFE tubes & boundary switches.  The Anycubic Kobra 2 has a long PTFE tube feeding filament to a direct extruder.  It makes it a lot harder to start a new roll of filament.  With a direct extruder, you have to pause the print, pull out the rest of the old filament, & put in the new filament. With the PTFE tube, you have to remove the PTFE tube to take out the last of the old filament.