This is a loaded question and a half, but what I always tell people is, buy the bike that is best suited to 90% of your riding. Lets break it down.
Leisure riding - If you're looking to commute anywhere from 5-20km each way, or looking for a bike to take on a mellow 45 minute ride around the pathways, I'd recommend a hybrid bike like the Trek FX or Specialized Sirrus. These bikes are characterized by an upright seating position, flat handle bars, and 700c wheels. They're ideal for fitness and leisure on paved or gravel pathways, bike lanes, and parks.
Road Biking - If you're looking to ride longer than 60 minutes on a regular basis, or have friends who ride road bikes and are just getting into road biking, I'd recommend an endurance road bike like the Trek Domane or Checkpoint, or the Giant Defy. When you get into riding those longer distances and durations, the versatility of drop bars and more aerodynamic body position allows you to ride more efficiently without relinquishing too much comfort. Road bikes like these are great for everything from bombing around town for leisure rides, or heading out for a 3 hour ride with friends on some quiet country roads.
Mountain bikes - Mountain bikes are characterized by smaller diameter, higher volume tires, front and/or rear suspensions, disc brakes, and more upright body positions. The transition from the instances where you may need a hybrid bike versus a mountain bike depends, but usually when you start straying away from gravel pathways and into narrower trails with rocks and roots  is when a mountain bike would be the best tool for the job.
Others - There's a whole range of other categories that I could get into but hybrids, road bikes, and mountain bikes account for about 80% of the bikes that most of my readers are interested in. I could get into niches like fatbikes, crusier bikes, touring bikes, gravel bikes, e assist bikes, but chances are if you're interested in those bikes, chances are you're a bit beyond this post already.
If you're still unsure which category you fall into, think about what your friends ride, and ask them questions about how and where they ride. Chances are you'll be riding with friends and family when this is all over so generally they'll be able to provide a bit of insight towards your decision as well.