The split option is available for categorizing online bank transactions, Ralph.
Please know that once you select a transaction from the For review tab, you'll find the split option in the lower right corner beside the Add button.
Please refer to the picture below for a visual reference.

When matching transactions, you can only match one from the For review tab to multiple transactions created within the system to prevent duplicates.
You mentioned that the AI option to match a debit card into a split option has disappeared. To determine if this is related to browser issues, let's perform some troubleshooting steps. Clear the browser's cache can restore the program to its default settings. Web browsers store cache to speed up loading data and images you frequently access. However, over time, this cache can become outdated and corrupt, leading to issues like this. You can also use other supported web browsers to access your QuickBooks Online (QBO) account.
I would love to introduce you to the QuickBooks Live Expert Assisted team. They're a group of experienced experts ready to help you smooth out your financial operations that fit your business needs.
I'll add this helpful resource to guide you whenever you're ready to match your bank or credit card statement with the recorded transactions in QBO: Reconcile an account.
Don't hesitate to reply to this thread if you have any other questions. We're always here to help.