Wow, that's a pretty broad question.
I believe your current bike (Velotric Discover 2?) can do trails and "a bit of offroad", as its tires are at least 2" wide. You'd probably want to stick to dry, hard-packed trails. You can deflate your tire toward the lower end of the spectrum, and you'll have more traction. Try that first, and bring something with which to re-inflate when you're done on the trails. You'll be surprised how well it does.
Once it gets soupy or with more loose sand and rocks, you'll want a bit wider tires with a bit more aggressive knobby tread; just realize this will slow you down on pavement.
Mid drive is not needed just because it is offroad. Mid drive can give more torque at lower speeds because it can use the bike's mechanical gears, so it's not just stuck with the one high gear ratio, like hub motors are. Mid drive are also more balanced, so they fly better. (this is another reason why the nicer electric mountain bikes are usually mid drive)
In the US, we have this brute force option, where we have a lot of 750 W hub motors on eFatties. The hub motor is so powerful that it makes enough torque at lower speeds in addition to high. We have triple the power available here, compared to the rest of the world, which is good & bad. On the good side, we have the option of more power. On the bad side, it encourages laziness in design. (more power = more torque without the need to re-design, and also allows power-focused advertising)
