How to extract flavour from fruit without heating it or using alcohol?

Simply, you don't. Your post describes a method which starts with whole fruit, doesn't use heat or alcohol, is achievable in a home kitchen, and has a high yield. Such a method simply doesn't exist.

Your assumption that "if the food industry does it, I should be able to do it too" is wrong. The food industry doesn't do it. It uses engineered flavors, which create the most salient smell molecules of a given fruit without using the fruit. If these are created using pure chemistry (such as isoamyl acetate for banana flavor), they are called artificial flavors, if they are created biologically (e.g. isolated from mold, as for strawberry flavor), they are called natural or naturally identical flavors. Methods for extracting them from the real fruit exist, but they are too expensive and inconvenient.

All methods which start with the whole fruit have roughly two steps, first extraction with a solvent and then concentration. The only two solvents usable in your kitchen are alcohol and water (the industry may use others such as CO2, but the technology is not available at home) and you excluded alcohol. As for water, you could in principle do something like a compote or a fruit tea, but as you are looking for high concentration, you are lucky that all the flavor compounds in fruits are already dissolved in water - so your starting point will always be fruit juice.

By the way, you can probably improve your yield here somewhat with a suitable juicer - a masticating juicer will give you more juice per unit of fruit than a centrifugal juicer. But it will be an incremental improvement, don't expect to get three times as much juice out of the same mango.

The second step would be the concentration. You are right that heating changes the taste, but that's the only method available in a normal kitchen. The other methods would be freeze drying and vacuum distillation. I haven't heard of even the hardiest food geeks getting freeze drying systems in their laboratories (I wouldn't call their cooking spaces "a kitchen"!), and rotovaps for vaccum distillation are used by maybe a handful of cooks around the world. There, you can assume costs of about 10 000 Euro for the whole setup (including pump etc.) and you need a learning curve.

And third, if the unchanged taste is so important to you that you decide to pay the 10 000, your yield will still be tiny. It is not just that you get a small amount of fruit juice out of the large amount of whole fruit, you have to still reduce it further to get an actual concentrated extract. There is no way around that, it's simple physics - there is just a small amount of real "flavoring" in each berry or mango, and you can't get our more than there was in the first place!

If you want to flavor things at home, the most accesible way would be to purchase flavorings used by the food industry. They are rarely available in their pure form, but you can buy flavored concentrates intended for drinkds, such as Tang. Instead of adding water, you can use them to flavor other things like cake glaze or lollies (be mindful of the other ingredients such as sweetener and acid when you do it).

Another, more expensive option is to purchase freeze dried fruit powder. It does pack a punch of flavor and color, and gives a better flavor than the drink powders. And because it is completely dry, you can use it in places like buttercream where a water- or alcohol-based extract would mess up the texture. They are of course expensive, because of the abovementioned low yield, the industry needs to use kilograms of fruit to produce a few grams of the powder. If you do this, decide if you always need the pure stuff - for the most expensive ones, there are also options of powders which use maltose as the base, giving you more bulk.

One way to do this would be to create a fruit slurry in a blender, mix in an enzyme (Pectinex), then clarify. Your highest yield would come from a centrifuge, but you can also easily use a method called agar clarification, with a fairly good yield, to end up with a clear liquid. You can then sweeten this liquid if desired. You could also thicken it with ultra-sperse or ultra-tex, which do not need heating to function. Of course, the issue here is that your final product will only be as flavorful as your original product. You are not going to create great tasting strawberry juice from crappy mass market strawberries, for example. Also, the result is not a concentrated flavor, but is useful as an add it. You could create a strawberry soda, for example. To concentrate the flavor, you will need to evaporate water. That means heat, and an obvious impact on the fresh flavor. It could be delicious, just different.

Generally you can amplify the flavor of fruit by adding both sugar and acid (i.e. lemon juice) to it.

If you want to end up with a liquid or jelly consistency you can simply mash the fruit, maybe run it through a sieve to remove seeds, and add both sugar and lemon juice. Most sorbets are made this way because the flavors are muted when they are ice cold so they are amplified first.

A trick for achieving this without actually adding anything is to remove some of the water from the fruit. The sorbets that you see that say "nothing added" usually start with the fruit and remove some of the water.