If you told me they weren’t GMOs I wouldn’t believe you because they grew so, so fast and they’re super resilient. I know chili plants are more resilient than other species, but I’ve never seen something like this.
However only one plant is giving me flowers, the others not yet. Can I do something to help flowers grow into fruit? Prune leaves, for example? I seriously have no idea about gardening beyond giving plants water and sunlight.
This, some peppers like habaneros take forever to flower and develop fruit. Chilis in general like full sun, summer is their time.
When I have a young plant flowering earlier than I think it should I prune the flowers so the plant can focus on growing big and strong instead of flowers too early. I’m not sure what’s the case here.
For some generic gardening stuff;
Adding some compost to the soil and tillage (like straw or something, I prefer no-till when I can) is good before transplanting/planting a plant. For the soil itself plants generally like something balanced that drains reasonably not too sandy nor clay-y. I would look up what that chili plant in particular requires and try to find a patch of that type soil around if possible. Can always mix your own soil using storebought mixes if you can’t find any good patches.
Also good to check what you have growing around too, some plants don’t play well together but others do. Where I live now no critters eat chili peppers (or they learn quickly why not to) so chilis make a good guard for my tomatillos which are much more appetizing.