My 1099-G unemployment compensation form for the year 2020 is not divided in boxes, it just contains the total payment and taxes withheld. How should i fill this in?

You should be able to figure out what boxes they go in.

You can  type  unemployment   into the search box at the top of your return and hit find.  It should give you a Jump To link to take you right to it.

Or Enter a 1099G for unemployment under

Federal on left

Wages & Income at top

 Unemployment - Click the Start or Update Button

For the withholding there might be a checkbox that says "Federal or state income tax was withheld on this payment".  You have to check it for the withholding boxes to show up on the next screen.