Cut off a piece of filament that's about a foot longer than your bowden tubing. Remove the bowden tube from the printer. Attempt to feed the raw filament through the tube by hand. If it's even remotely difficult, you've got an issue. There should be next to zero friction. If it isn't difficult, extrude that same length of filament through the extruder gear (the end goal is you want the filament to be chewed up by the gear). Attempt to push the chewed up filament through the disconnected bowden tube by hand. If the chewed up filament is now difficult to push through by hand, it means either your idler force is too high, or that your drive gear tooth profile is too aggressive. It appears you're using a straight toothed pulley on your drive. Regular gear teeth are generally pretty bad in bowden systems because they bite into the filament so aggressively, and it causes a lot of friction in the bowden tube. If this is the case, consider switching to a MK8 hobbed pulley to drive your filament. It is essentially the go to drive pulley used on many new printers because it has very good grip, little backlash, and it barely even leaves a mark on the filament.

If you don't encounter any friction in the tube (raw filament or chewed up) consider:

• What voltage is being supplied to the extruder motor? Too low a voltage = skipped steps. But don't just crank that driver up because you'll fry it.

• What material/ temp are you printing? Ungeared bowden extruders generally aren't the best at extruding at colder temps.

As a misc side note, also consider that you want the bowden tube to be as short as possible. Your length looks OK so I doubt it's a major issue.

I'll throw more on this comment as it comes to me, but that should get you started.