Are you trying to split a transaction in the Banking Add/Match feed screen?
If so, it’s not possible at that point, you must go elsewhere to do this.

The simplest solution is create an Expense.

Goto > + > Suppliers > Expense

This will open a blank Expense Page which allows you to choose […]

Resolution for 'blank Expense Page issue: 'Where is the split function when you are paying something like a credit card and need to categorize various expenses differently?' available: Yes.

The blank Expense Page issue or error code is a known issue in Quickbooks Online (QBO) and/or Quickbooks. Support for this issue is available either by self-service or paid support options. Experts are available to resolve your Quickbooks issue to ensure minimal downtime and continue running your business. First try to resolve the blank Expense Page issue yourself by looking for a resolution described in the article. If it is a complex blank Expense Page issue or you are unable to solve the issue, you may contact us by clicking here or by using other blank Expense Page support options.

For more information about resolving issues related to blank Expense Page in Quickbooks/QBO or to get support for the issue 'Where is the split function when you are paying something like a credit card and need to categorize various expenses differently?', click the link below: