Getting to know the folks at a local bike shop would be my first recommendation. If it's a decent shop they'll steer you in the right direction.
REI is another good recommendation but they are fairly limited on model selection and sizing due to the bike footprint in their stores. In low-mid models they carry a lot of their house brand (Co-Op Cycles) and some Cannondale. They also carry some higher end stuff.
A couple of things I've learned in my own bicycle adventures recently:
1. I rode bikes with 26" wheels for decades. 5 years ago I bought my first mountain bike with 27.5" wheels. It was that or 29" and this one with 27.5's really stood out to me. Larger wheels are a game-changer on the trail as well as on paved paths and street riding. Just feels better, IMO. More stable, easier to roll over small bumps. I also have a 29'er now, and it's even more capable than the 27.5. I prefer WIDE tires but not fat for everyday use. My 27 is a 2.8" wide tire and it looks huge. It cushions the ride and feels super stable even if it's a little chunkier/heavier.
2. Modern everyday and mixed-terrain bikes generally have more "slack" geometry and wider handlebars. They feel amazing compared to older geometry. Definitely ride a bunch of different bikes!
3. Electric bikes aren't just for the lazy. Even if your goal is fitness, an E-bike will help you go farther, longer, and it's there when you need a boost, or, if you're still working on your fitness. You don't want to dread bicycle commuting or workouts because of a hill that always gives you trouble or feeling completely depleted by the end of the ride!
4. In the everyday and trail/mountain categories most drivetrains have moved to a single front sprocket with 7-9 speeds in the rear. IMO this is a much more efficient setup than an 18 or 21/24 speed setup of old, and it reduces weight.
5. Disc brakes are becoming fairly standard. Absolutely worth the spend!
