I appreciate you posting here in the Community, @Biker Sue. I’m here to share some insights about running payroll and creating P45 for your leaver.
To begin, mark the employee as a leaver. Just open his/her profile, tap the down arrow under his name, and select Mark as leaver. You’ll be prompted to enter the Leaving date and the Reason for leaving.
Since you don’t want to run payroll in advance for all of your employees, you'll have to skip the submission and rollback the payroll and re-run with the final figures for all of them. You will then be able to make a submission after this.
For the leaver, you'll need to manually edit or enter his/her final payment. To do so, you can go to the Payroll menu and select the employee. After that, you can view and print the P45 form. Here's an article that'll guide you with the process.
For more details, you can check this article to manage an employee status in QuickBooks Online Standard Payroll.
You can also visit this link to view and print payslips.
The Community is always open if you have other payroll concerns. Feel free to leave a comment down below. Keep safe!