It's great to have you here in the QuickBooks Community, @kvndaniel38.
There are a few possible reasons why the invoice number field is missing on the invoice page.
First, the custom transaction numbers are off in the settings. To check, please follow the steps below.
Go to the Gear icon and choose Account and settings.
Select Sales.
Navigate to the Sales form content section and click the Pencil icon.
Check if the Custom transaction numbers are toggled on.
Click Save and Done.
Second, the Invoice no. is off on the invoice page. Here's how to check it.
Go to +New and choose Invoice.
Select Manage, then click Customization.
Check if the Invoice no. is toggled on.
If everything is on and the invoice number field is still missing, this may be due to your browser's cache being full. You can troubleshoot your browser by referring to this article: Troubleshooting browser problems.