Can Opening Balances Be Entered in the General Ledger (Assets, Liabilities, and Equity Accounts)?

Yes, when you start using the system, opening balances are entered using an intermediary account called Opening Balances, and they are recorded manually through journal entries as follows:

First Entry:
From: Asset Accounts
To: Opening Balances Account

Second Entry:
From: Opening Balances Account
To: Liability and Equity Accounts