Question about debt

So I have recently gotten into monetary theory. Basically, transactions in the world of fiat are pretty much all just debt being thrown around in the form of government currencies or bank deposits. This means that most transactions change the amount of debt and thereby the amount of money in circulation.

Now, my question is this: Since many coins has a fixed supply but can be lent out, is there a way of knowing how much there actually is including the debt? Do you know any reliable data sources to find out how much bitcoin (or other crypto currencies) have been lent?

I think this might be especially interesting for DeFi since I wouldn't be surprised if a large amount of ETH for example might be borrowed multiple times. That's kinda what yield farming is about right? Also any form of investing on margin.

Not trying to offend anyone here, really just looking for data or other input.