If your OKX portfolio in Delta shows fewer assets than your OKX app, the missing assets are most likely held in OKX Earn.
OKX Earn is not currently supported by Delta's Exchange Connections, so those assets won't be imported automatically.
Workaround
You can manually add the missing balance to your portfolio using a manual transaction. Tap the "+" button in Delta, select Add Transaction, and enter the amount held in OKX Earn as a manual buy or holding.