I can share some information about importing data in QuickBooks Online.
Yes, the option to import invoices is available in the free trial mode. However, please note you can only import a maximum of 100 invoices at a time and 1,000 row limit per spreadsheet.
In case you need the steps, here's how:
Click the Gear icon in the upper-right corner.
Select Import data under Tools.
Choose Invoices.
Press Download an example if you need to view the format.
Upload your file by pressing the Browse option and selecting the CSV file.
Hit Next.
Map the fields until finish.
Additionally, here are some helpful references that you can check out about the import process, like what information you can include in the spreadsheet, as well as importing templates: