You can fix this if you start doing other stuff. Yoga, swimming. Walking more.

Also just take breaks from sitting once in a while. Stand up every hour or so.

I thought that pose was just used by females to appear more curvy, can't say I studdied the few males but my office sitting position looked closer to Thoracic Kyphosis.  Not sure if that's better or worse...

I have #2 and 3. I'm just going to get an inversion table and hang for an hour a day to fix it.

Can literally just stretch and be fine lol.

Same.

I can't wait to see your upside down desk setup

Hahahaha. Nicely done.

Supposedly strengthening the abs and the buttocks will have some effect. I've never been able to fix mine, but I'm not sure there's really any benefit to fixing it besides appearance (it makes the gut look big).

I read something a few months ago where a study showed that certain athletes exhibit this posture naturally. Sprinters were an example of this, which makes sense because angling the pelvis downward increases the range of motion of one's stride.

Forward leaning shoulders is an issue that I have as well, which I've been to correct somewhat via strength training and volitional posture correction. I think this is actually important to correct because it actually displaces the joint (the shoulder is mostly held in place by soft tissue).

The thing that REALLY catches my attention is why 90% of people have duck feet. Have you ever noticed that? People literally walk with their toes pointed 45 degrees outward. I can't do that without limping.