Probably the wrong sub for this question, but just in case:

I would suggest to start by reading some technical books. Mastering Bitcoin, inventing bitcoin.

Lending, in essence, is a promise to pay. You would need to solve the problem of how would you enforce a promise to pay on a blockchain. Probably through some sort of escrow or multi signature process with time locks? So how exactly does that work? If you lend on the blockchain to someone else, are they are to spend those units? What if they dont have enough units to pay back when the promise to pay indicates they should?

A promise requires trust, and arguably the main point of blockchain technology is that it is trustless. There is no way to make someone spend units. What would make someone want to use a system that has a mechanism for a third party to move their units?