I know you said you have a US keyboard and "US English settings," but this sure seems like a localization problem of some sort. TurboTax is strictly a U.S. tax program. It's designed to run on U.S. computers, and does not work with other region, language, or localization settings. I gather that you are not in the United States, so maybe something you are doing to adapt to your location is contributing to the problem you are having.
Do you have multiple keyboards on your computer? If so, when you are using TurboTax, click on the language icon on the taskbar and make sure that English (United States), US Keyboard is selected.
Please double-check all of the following settings, just to be sure. Something obscure might have gotten changed accidentally.
Go to Settings > Time & Language > Region.
Country or region should be United States.
Regional format should be English (United States).
On the left side, click Language.
There are several icons at the top of the Language panel. They should all say "English (United States)."
Windows display language should be English (United States).
Under Preferred languages, is more than one language listed? If so, English (United States) should be first in the list. If it's not, click on it and move it up to the top.
Click on the Keyboard icon at the top. On the Keyboard panel, "Override for default input method" should say "Use language list" or English (United States) - US. This is assuming that English (United States) is at the top of the Preferred languages list.
Is the box checked that says "Let me use a different input method for each app window"? I don't know how that works. If that box is checked, you have to make sure that you are using English (United States), US Keyboard in the TurboTax window.
Go back to Region. On the right side, scroll down a bit to Related settings and click "Additional date, time & regional settings." This will open a Control Panel window. In the Control Panel window, click on Region. At the bottom of the Region window, click "Additional settings."
On the Numbers tab, check all of the following. The period and comma can be hard to see, especially on a laptop screen. Look very carefully.
Decimal symbol: . (period)
No. of digits after decimal: 2
Digit grouping symbol: , (comma)
Digit grouping: 123,456,789
On the Currency tab, check the following.
Currency symbol: $
Decimal symbol: . (period)
No. of digits after decimal: 2
Digit grouping symbol: , (comma)
Digit grouping: 123,456,789
