How to check the background forms from TurboTax online app

You do not have direct access to forms with online TurboTax.   Forms modes is a function in desktop software.   You can see your Form 1040, and then after you pay your fees if you want to print  a copy of your return for review before filing you can do that

PREVIEW 1040

https://ttlc.intuit.com/questions/1901539-how-do-i-preview-my-turbotax-online-return-before-filing

Click on Tax Tools on the left side of the screen. Click on Tools. Click on View Tax Summary. Click on Preview my 1040 on the left side of the screen.

https://ttlc.intuit.com/community/printing/help/can-i-print-a-copy-of-my-turbotax-online-return-before-i-file-it/00/26244

Using the TurboTax online editions there is no direct access to any of the forms, schedules or worksheets included with your tax return.  That is only available using the TurboTax desktop CD/Download editions using Forms mode.

However, you can view your Form 1040 at any time using the online editions. Click on Tax Tools on the left side of the online program screen. Click on Tools. Click on View Tax Summary. Click on Preview my 1040 on the left side of the screen.

To view/print/download the tax returns for your account before filing you would need to pay the TurboTax account fees.

To pay the TurboTax online account fees by credit card, without completing the 2021 return at this time, click on Tax Tools on the left side of the online program screen. Then click on Print Center. Then click on Print, save or preview this year's return. On the next page, to pay by credit card, click Pay Now. The next screen will show a review of your Fees, click on Continue. Complete the next screen to pay by credit card and click Continue