Glad to see you back in the Community, @Fiat Lux - ASIA.
I'm here to give you some insight into the Profit and Loss report.
The reason why you're not seeing the expenses distributed to each class is that you have unclassified COGS. You'll need to create Chart of Account with the type as COGS but the name based on what you're using for that Chart of Account.
Based on my visual guide below, I can see the expenses related to the class. The highlighted part is the Chart of Accounts that are COGS but named differently.
In my list of Chart of Accounts, you'll see the different named COGS.
If you're wanting to individually show each expense (paychecks, bills, etc), then you'll need to run the Transaction Detail by Account report.
Here's an article that can give you more information about the Chart of Accounts.
If you have any additional questions, don't hesitate to ask. I'm here to lend a helping hand. Have a splendid day.