It’s true that the latest version has removed the concept of starting balances from the program. New approach is to simply create transactions to establish these balances which many businesses had to do anyway because starting balances could not capture everything required.
For example, even single inventory item could have number of starting balances. Qty on hand, qty to receive, qty owned, qty to deliver etc. To establish quantity to receive or quantity to deliver, you’d need to enter individual sales and purchase orders.
If you need to set up Qty Owned starting balance, you have number of options but the most straightforward one would be to record a journal entry where you select account Inventory On Hand, then inventotory item, enter quantity and total cost.
Balance can be posted to Retained Earnings account.
Typically this journal entry would contain starting balances for all your accounts, not just inventory items.