Among all the other good answers I'd like adding one more thing:

Choose the appropriate bike to your style.

Every bike is a compromise. Some are best for one purpose and nightmare at others, some are somewhat okay-ish for most purposes. Wrong combination of expectations and desires, and bike design choices leads to frustration.

I would strongly recommend starting with a decent used hybrid or gravel bike, see below, because they combine reasonably both road and off-road performance. After some time (years) in the saddle you'll find what you actually like and you can go for more targeted option.

• Choose road bike if you love riding on tarmac and other hard and smooth surfaces fast and light. Such bikes are super light but with little to no cargo capacity*. Outside the roads they are poor (dry, solid mud) to nightmare (wet grass, wet mud). The question off the road is not "Whether I get a puncture" but "when I get a puncture". Most of those have drop bars so your position will be optimized for aerodynamics but compromised on handling.
• Choose mountain bike (MTB) when you love riding on rough terrains like gravel, mud, dirt in maintains. On "smooth" gravel/dirt they are okay-ish but on tarmac they are nightmare to ride. The full suspension frames are great for downhill rides but waste a lot of energy otherwise, rigid bikes are most efficient but hard for your hands and butt. Hardtails are good compromise because they smoother the ride for your hands while your legs can damp the hits from the rear wheel. Hardtails and rigids have higher cargo capacity if it matters to you. These have quite wide straight bars, so you have better cont perrol of the bike but less aerodynamic posture.
• Choose hybrid bike if you want to combine the surfaces with more of easy off-roading and a bit less of tarmac. These bikes combine good off-road maneuverability and reasonable drag on tarmac. Handlebars are a bit narrower compared to MTB so the posture is more comfortable.
• Choose gravel bike if you think of a hybrid but want more of the tarmac road and the drop bars.

All those above are performance oriented, meaning you want to cover long distances at once. You somewhat need to learn the comfortable and efficient position and set the bike properly.

There are also other bikes that focus for other purposes:

• BMX are for stunts and stunt tracks.
• City bikes are focused on comfortable ride around the city centres. The posture is comfortable but tiring on long rides.
• Cruiser bikes are more comfortable and a bit stylish.
• Single-speed / fixed gear bikes are optimized for reliability (If it's not there, it cannot break) but they are horrible in steep uphills and off the road. Hardcore fixies (no brakes) are for hipsters.

Almost every style has its e-bike version. They are great for those who want to prolong their "biking career". I would not recommend them to people with little-to-no expirience with bikes. They help only with the power and nothing more but at the expense of lower control (traction lag, power misballance) and weight (different braking styles, different centre of mass).

(*) I have bought Specialized Allez road bike and I'm abusing it off the road and with rack and panniers. It is fun to push it beyond the limits, but I'm much slower off the road than my SO on their gravel bike (which would have been much wiser choice).

Among all the other good answers I'd like adding one more thing:

Choose the appropriate bike to your style.

Every bike is a compromise. Some are best for one purpose and nightmare at others, some are somewhat okay-ish for most purposes. Wrong combination of expectations and desires, and bike design choices leads to frustration.

I would strongly recommend starting with a decent used hybrid or gravel bike, see below, because they combine reasonably both road and off-road performance. After some time (years) in the saddle you'll find what you actually like and you can go for more targeted option.

• Choose road bike if you love riding on tarmac and other hard and smooth surfaces fast and light. Such bikes are super light but with little to no cargo capacity*. Outside the roads they are poor (dry, solid mud) to nightmare (wet grass, wet mud). The question off the road is not "Whether I get a puncture" but "when I get a puncture". Most of those have drop bars so your position will be optimized for aerodynamics but compromised on handling.
• Choose mountain bike (MTB) when you love riding on rough terrains like gravel, mud, dirt in maintains. On "smooth" gravel/dirt they are okay-ish but on tarmac they are nightmare to ride. The full suspension frames are great for downhill rides but waste a lot of energy otherwise, rigid bikes are most efficient but hard for your hands and butt. Hardtails are good compromise because they smoother the ride for your hands while your legs can damp the hits from the rear wheel. Hardtails and rigids have higher cargo capacity if it matters to you. These have quite wide straight bars, so you have better control of the bike but less aerodynamic posture.
• Choose hybrid bike if you want to combine the surfaces with more of easy off-roading and a bit less of tarmac. These bikes combine good off-road maneuverability and reasonable drag on tarmac. Handlebars are a bit narrower compared to MTB so the posture is more comfortable.
• Choose gravel bike if you think of a hybrid but want more of the tarmac road and the drop bars.

All those above are performance oriented, meaning you want to cover long distances at once. You somewhat need to learn the comfortable and efficient position and set the bike properly.

There are also other bikes that focus for other purposes:

• BMX are for stunts and stunt tracks.
• City bikes are focused on comfortable ride around the city centres. The posture is comfortable but tiring on long rides.
• Cruiser bikes are more comfortable and a bit stylish.
• Single-speed / fixed gear bikes are optimized for reliability (If it's not there, it cannot break) but they are horrible in steep uphills and off the road. Hardcore fixies (no brakes) are for hipsters.

Almost every style has its e-bike version. They are great for those who want to prolong their "biking career". I would not recommend them to people with little-to-no expirience with bikes. They help only with the power and nothing more but at the expense of lower control (traction lag, power misballance) and weight (different braking styles, different centre of mass).

(*) I have bought Specialized Allez road bike and I'm abusing it off the road and with rack and panniers. It is fun to push it beyond the limits, but I'm much slower off the road than my SO on their gravel bike (which would have been much wiser choice).