For potatoes, you quote 25 sqft per person, which seems to be 2.32 square meters.
The maximum yield for full industrialized production is 40 000 kilos per ha, 10 000 sqm, 4 kilos per sqm
Like these claimed results of 105 kilograms of potatos grown in 6 square meters, which works out to 17.5 kilos of potato produced per square meter.
I grew 235 lbs Of Potatoes in 200 sq ft Without Wateringhttps://www.youtube.com/watch?v=JrytUqXE9Ns235 lbs is 106 kg
200sqft is 18.5 sqm
It gets you 5.7 kg per sqm, nothing out of the ordinary for somebody who does this in order to get results.
While plants do technically grow out of thin air they still need nutrients to grow that big fruits or tubers or else, your average garden without aid won't be able to produce 20 kgs/sqm unless much of that is water, like cucumbers. And you can't live on cucumbers
I wonder what you tried to do with yours that went wrong, potatoes are quite resilient in growing, it takes art to mess them up . My specialty is growing cabbage with leaves opened up like a sunflower and harder than bamboo!
I honestly don't bother much with strawberries🍓, they grow without too much effort - although I always plan to get as many varieties as possible and pay a little more attention to them. Since I'm allergic to something that producers spray strawberries on (and other fruits and vegetables), this is the only way I can eat them without looking like I've been stung by bees or wasps🐝
I wouldn't use herbicide either on small plants with short flowering fruit cycles but you could help them a lot with a weed barrier. Obviously not that cheap HDPE or PEHD or whatever poly- thing but one sheet made out of wool and wood resin. Not going to last more than 4 years as it does discompose but nothing to worry about them either. The problem with weeds is that once you get some nasty stuff like knotgrass it will be a pain in the ass to get rid of it, you're going to feel the need to buy a flamethrower.
Back to the main topic, did a bit of math on those assumptions.
This source claims an average of 200 square feet is needed to produce adequate food for 1 person.
7 billion means 1.6 trillion sqft, so if the online convertor is right this is about 57392 square miles so we could feed the entire world if we raze Georgia to the ground and make it all agricultural land.
The metric system is simpler, 18.5 m2 per person, 148 000 km2, so ~ Sweden or Spain, and we have land for beaches and resorts left.
Seriously doubts those claims, it would mean Lesotho would be needed to feed the whole of Africa.
If you can't see that tiny green dot there, I don't think you can see any reason to believe the claims either.