To your original question about differences between full susp and hardtail, I'd say yes and no.
If all you have ever ridden is a full suspension, going to a hard tail takes some adjustment. Your legs and arms become the suspension and get put into use a lot more whether climbing or descending. You spend much less time with your weight fully on the saddle. With a full suspension putting weight on the saddle helps how the suspension works - that's part of why when you set up sag on a full suspension you sit with all your weight on the saddle. On a hardtail, that saddle needs to have some room to move beneath your butt so it doesn't kick and jostle you around. I also find that without the rear suspension keeping the rear tire in place your arms get used more to help keep the bike in line. As others have mentioned above, a full suspension will do a better job of saving you from your mistakes.
The "no" part of my answer is that it only takes a few rides to realize and practice the differences after which switching back and forth takes no real thought.
Good to read that you brought your air pressure down from 40 to 20. 40 psi on a Stache is ridiculous. I probably wouldn't have my pressure that high if I was just riding a paved rail-to-trail path to the local brewery. If you haven't done so already, set up those tires tubeless.
Kudos to you for taking up mountain biking at such and advanced age (purely tongue in cheek; I turn 54 on Thursday). But based on just the very few words that you've written here I'd suggest you find some friends, a club, a bike shop, or similar to help you gain some more skills and knowledge. A 20 inch drop is not considered very technical. Get a friend or two to take you out to that same drop and session it for ten or fifteen minutes. Watch how they are riding it then do it yourself several times over. Then go do the same with some log overs, rock gardens, creek crossings, etc. etc.
Cheers. Keep riding. Keep learning. Make sure insurance is up to date. ;-)