The reason you can't borrow money on the Cash App could be - if you have an outstanding negative balance on the Cash App Wallet, you haven't verified your Cash App account, your account has violated the TOS, and Your Cash App mobile app has not been updated to the latest version.
Even if you meet all the above requirements, we don't know how Cash App lending facility is made available and what criteria is there for anyone to be able to borrow money on Cash App is done.