Darklang is utilized for "deployless" backends. "Darklang" is probably not as intimidating as it sounds - the demonstration videos certainly don't make it seem like it is. You basically hook together web services - sort of like Zapier or Microsoft Power Automate - in such a way that a lot of the wiring of what we know to be the back-end is handled for you.
Naturally, the company behind the technology is only taking offers to manage the back-end for paying customers.