The market for fixed-yield protocol debts is called Copra. The original purpose of their fixed-rate loan is to assist other DeFi protocols in raising protocol-managed liquidity, which they can then utilize to 1) increase protocol income by taking the yield spread from successful strategies, and 2) bootstrap new pools without being dependent on excessive token emission.
Although Copra doesn't currently have its own token, it is one of TVL's protocols that is expanding the fastest, and it has made references to a potential airdrop. If a user's token goes live, they can be eligible for an airdrop through the platform for lending tokens. To improve your odds, finish their Zealy tasks as well.
https://www.copra.finance/app