https://i.pinimg.com/originals/59/6f/f6/596ff65c7f781fc1ec465c684993d452.jpg

https://i.pinimg.com/474x/f3/65/1e/f3651e10df09ebdf63acf701720416f9.jpg

or this https://everythingbackyard.net/wp-content/uploads/2017/10/dead-man-anchor.jpg

You dont want the cable to be stretched against a 90 degree corner on the wood post, so no hole in post with cable run through it. The cable elongates and retracts in size, it also stretches from bearing weight. Rubbing against the wood over time will deform it and weaken it. Putting it on an upside down pully as shown in one of the images above would work better. Or looping a chain around the post and then attaching to that with a hook and turn buckle would be what I prefer on my build. You tighten the turn buckle to account for any changes in cable length. It gets surprisingly smaller during colder times.

I prefer an A frame, you need 300lbs of concrete atleast in a 2ft radius of a foundation, buried about 2 feet of dirt so there is no movement. Two 2x4 kickers from the foundations out at a 45degree angle to the top of the 6x6 post.

Doing a single 6x6 post at a slight angle forwards with an pully at top, with the cable running over and behind, attaching to a 300+ lb concrete foundation buried a ways underground is the most efficient, I just dont like it for some reason.

googling zip line post and looking at the pictures would give you more help than making this post.

no