@pablob You probably have long arms and weak lats and supporting back muscles(rotators, lower traps, etc.). At 6'6" I've been where you are.
Dead hangs for a few minutes every day, scap pull ups where you just dead hang and retract your scaps a few inches every day, rotator cuff strengthening exercises a few times per week, and other activation and contraction work on lats a few times per week will get you to doing pull ups in likely weeks, but at most a month or two.
Here is a little routine...
Rotator Cuff Work, light resistance:
Band Pull Aparts 3x10
Band Row full ROM protraction to retraction 3x10
Band Internal/External Rotations 3x10 each
Serratus Push Up 3x10
Serratus Wall Walk 3x
Bodyweight from Pull Up Bar:
Dead Hang 3:00 Total in whatever intervals you can, even :10-:20 at a time, or even with partial assistance from the ground if you need at first. Can mix up grips.
Scap Retraction Pull Ups 3x10
Machine, medium resistance:
Lat Pulldown Machine 5x10 - I know it is BW Fitness but this is to help get you started on activation and contraction of the main mover in pull ups, your lats. Once you progress to the point you can do pull ups then you can ditch the assistance of the machine and do pull ups on your own. This is a means to an end