Ok so I have never done this and my main concern is the area I want to hit is right behind the o2 sensor is it safe to pressure wash it

Don't pressure wash it. Spray an extremely liberal amount of simple green on it, then just rinse that off. Pressure washing can cause water to get into electrical components and cause corrosion. Also, keep water away from stupidly obvious places like the fuse box

X2 on the no pressure washing, I cut up grocery bags and zip tie over the distributor, throttle body, Fuse/relay box and anything else under the hood I don't want to get wet.. The use some sort of degreaser then rinse with a hose.

use spray on engine cleaner and a hose, no pressure washer, it is not a dirt bike

Buddy of mine told me oven cleaner will eat the grease off it but that will eat paint but I have like a quarter inch of mud and oil from a leaking valve cover gasket so might just do it and then paint the engine...

Id stay away from that. That stuff has serious corrosive attributes. Just use degreaser and actually hand wipe the stuff that's really thick and caked on.

Ill strive away from it but don't forget...easy off makes the best pepper spray lol

Alternator, throttle position sensor and distributor cap do NOT play well with water. Protect them properly before you do this.

And don't be overly concerned about doing a perfect job. Personally, I avoid direct spraying on the top of the engine.

A bit of grease is not going to hurt anything.

and it will keep the rust away...

The only negative aspect is it does cause the engine to run a little hotter. Especially on the older closed system Cherokees. Speaking from personal experience. I pressure washed mine with no side effects and now my jeep runs about 10 degrees cooler. I had alot of oil and crude on my block

Generously spray all the nasty spots. Let it sit for as long as possible.
GENTLY hose it off, not too much water or pressure. Repeat as needed.

Remember, all that nasty stuff is going to come off so don't let it run off into my trout stream. Do it on a flat gravel, sand driveway or parking pad.
The Simple Green will, over time, help break that stuff down.

You could also use a bunch of pages form the New York Times, Washington Post or Atlanta Journal Const to wipe off the grease.