Does modern lifestyles endanger our health?

Because "lifestyles" is plural it should be "do" rather than "does." For example, "Do ants like honey?" "Does that dog like to play?"

Nowadays we have access to great variety and quantity of natural food from all over the world, but the industry also produces more processed food than ever whatich is not as good for our bodies.

Even though we are free to choose the type of food we eat, generally speaking processed food is more palatable and manufacturers publicize it more because it is cheaper to produce and more profitable for them.

Similarly to the food, these days we have more spare time and we could choose to spend part of this time doing physical activity, besides we have easier access to gyms and sport facilities.

Or "similarly to food".

But, ion the other hand, the audiovisual entertainment on offer is massive causing many people to become couch potatoes.

Note that "audiovisual entertainment" is a very formal phrase while "couch potatoes" is quite informal, so it's a bit odd to see them in the same sentence.

In addition to that, modern jobs tend to be more sedentariesy, we have switched gardening tools for computers and chairs.

Although in many countries we are wealthier and (we) have more comfortable lives than earlier generations we are not improving our health.

You don't necessarily need to repeat "we" but your sentence is still correct with the repetition.

Nowadays we have access to a great variety and quantity of natural food from all over the world, but the food industry also produces more processed food than ever, whatich is not (as) good for our bodies.

Even though we are free to choose the type of food we eat, generally speaking, processed food is more palatable and manufacturers publicize it more because it is cheaper to produce and more profitable for them.

But, ion the other hand, the audiovisual entertainment offer is massive causing many people to become couch potatoes.

In addition to that, modern jobs tend to be more sedentaries, wy. We have switched gardening tools for computers and chairs.

In conclusion, I think that in general, therms modern lifestyle is damaging our health, but we have enough information and options to follow healthier lifestyles, we just need to make good decisions.

Does modern lifestyles endanger our health?

Although in many countries we are wealthier and we have more comfortable lives than earlier generations, we are not improving our health.

Nowadays we have access to a great variety and quantity of natural food from all over the world, but the food industry also produces more processed food than ever, whatich is not as good for our bodies.

*but the industry
"the industry" is too vague here, so you need to specify which industry it is.

*what is not as good
You could also have said, "...than ever that is not as good for our bodies." However, the sentence was already a little too long, so "than ever, which is not as good for our bodies" is better.

Even though we are free to choose the type of food we eat, generally speaking processed food isprocessed food is, generally speaking, more palatable and manufacturers publicize it more because is cheaper to produce and more profitable for them.

*generally speaking
Putting this here works just fine in oral speech. But in writing, it's grammatically awkward and works better after the verb.

It's partly because "generally speaking" clashes with "even though". You generally want to use one phrase like this at a time in a sentence, e.g. "Even though we are free to choose the type of food we eat, processed food is more palatable..." or "We are free to choose the type of food we eat but, generally speaking, processed food is more palatable..."

Similarly to the food, these days we have more spare time and w. We could choose to spend part of this time doing physical activity, and besides, we have easier access to gyms and sport facilities.

*similarly to the food
You could also say "similar to the food situation". Either way, when using "similar to," it's important to make clear exactly what comparison you're making. In the original sentence, it wasn't clear what two things were being compared.

But, iOn the other hand, the audiovisual entertainment we are offered is massive, causing many people to become couch potatoes.

*But, in the other hand
You only need one of these ("but" or "on the other hand").

*the audiovisual entertainment offer
"the audiovisual entertainment offered" or "the audiovisual entertainment on offer" would also work.

In addition to that, modern jobs tend to be more sedentaries,y - we have switched gardening tools for computers and chairs.

*sedentaries, we have switched
Without a conjunction, these needed to be two separate sentences. You could also write "...sedentary, because we have switched..."

In conclusion, I think that in general terms modern lifestyle is generally damaging our health, but we have enough information and options to follow healthier lifestyles, w. We just need to make good decisions.