Random thoughts here:

I also do nearly all of my hiking and backpacking alone. However, I have many years' experience in the back country behind me.

Since my pace is quite a bit slower than most, I've found that I'm actually safer alone. With a group, I'm always pushing to keep up, which makes me more prone to falls and accidents. I'd rather go at what is a comfortable pace for me, and that's no longer 2-3 miles per hour, more like 1 to 1 1/2. I do not need the anxiety of knowing that other people are either way out ahead of me waiting or that they are deliberately slowing their pace so I can keep up.

Since I am alone and am therefore more vulnerable, and since I'm well aware that at my age even a minor accident will probably end my hiking career for good, I am extra careful.

I always leave an itinerary with a family member who (1) can be trusted to call at the specified time if I'm overdue and (2) will not panic and call if I'm just a few minutes late. I specify a specific time to call if she hasn't heard from me, usually 24 hours later than I plan to come out (I'm always prepared for that much delay and it wouldn't be unusual--I've also been known to come out a day early). Since many trailheads have no cell phone reception, I always allow plenty time for me to drive out to where I can call. In some cases that's not until the nearest town, which may in some cases be several hours' drive from the trailhead. When in doubt, for planning purposes I assume no cell phone reception except within a few miles of towns.

I carry a PLB in case of serious emergency. Like the "ten" essentials, it comes with me when I'm way from camp fishing, finding water, etc. The chances are therefore excellent that if I'm past the 24 hours after I said I'd emerge and I haven't pushed the button, that I'm just running that much more behind schedule, or that my car broke down. The only other likely possibility is that I'm dead!

I will go off-trail if it's easy off-trail (no more than easy Class 2) and I've indicated it on my itinerary. There is quite a bit of off-trail travel that involves following officially abandoned trails still in use or various "use trails," some of which are more-used than the official Forest Service version, and don't involve anything more strenuous than sharpened navigation skills. I always go well off-trail to find a camp site and, in case of a lake, generally prefer to camp in the less-impacted areas near the inlet or outlet. If the off-trail stretch becomes too difficult, I turn around.

Like W_D, I'm pretty much of a loner and prefer it that way.

And also like W_D, I don't consider traveling a well-populated trail (to me that's where you regularly meet 3-4 people in a day) to be traveling alone.

As with every other aspect of hiking and backpacking, for going solo start slowly and work up. First, acquire plenty of experience--a lot more than you think you need--with all your gear and your navigation skills in all sorts of conditions and weather. If you've had no experience being stuck in a three-day storm in the high Rockies which ends with 6-8 inches of snow and then a night down to 10* F, going alone is not the time to learn to cope. Ditto backpacking for several straight days in our steady Pacific NW rain.

Second, once you have a good fund of experience, start with short overnight trips (close enough to the trailhead that you can easily bail out) and work up from there. Stick to well-populated trails. Do be more cautious and remember that alone you're more vulnerable. If you acquire new gear, start by testing it thoroughly, first in your back yard or car camping in a nearby state park, then on short overnight trips. Pick bad weather for some of those testing occasions!

As for finding people to go with: generally you'll find any number of hiking clubs and a number of meetup groups in and around the nearest population center of any size in your area. Google (or other search engine) is your friend! That's a good way to gain experience with a group and meet potential hiking/backpacking partners. That's what I did when I started getting really into backpacking after my kids were grown and were no longer around (or just not available) to go out with me.