How to record business expense paid by owner as Shareholder loan?

create a liability account called something like shareholder loan - [name]

use an expense transaction

line one, the expense account for what you are paying for and the amount

line two, the shareholder loan account and the same amount as a negative number

save the zero dollar transaction

later pay the loan

When you want to track the Actual Payee, it is much easier to make bank account and name it Petty Cash. Now you use Banking menu > Write Check, from the Petty Cash Account, to enter the purchase details individually by date, names, items, amounts, etc. At the end of this Date of spending, this account is negative. You use Banking menu > Make Deposit, and there is no Name to enter here, and the "from" account is Shareholder loan, for that amount to bring the Petty Cash Bank back to 0 for this date. Then, reconcile it, using ending balance of 0. That reflects you made your entries, you confirmed the offset to Loan, and you are verified to 0.