Why didn't Turbotax prepare a Form 2210?

Do you have a penalty on 1040 line 38?  I wouldn't worry about it.  The IRS can send a bill if they think you owe a penalty.  But it's better not to give the IRS any forms or info they don't need.  Wait for them to ask for something.  

You didn't give anywhere near enough information to evaluate your situation. But take a look at the top of Form 2210, at the flowchart that says "Do You Have To File Form 2210?" There are several situations for which it says "Don't file Form 2210." You probably fit into one of those situations. The IRS has enough information, without the form, to know that one of those situations applies to you. And TurboTax knows if one of those situations applies, so it doesn't prepare the form. You don't want to file the form if the IRS is telling you not to file it.

I don't have a penalty on Form 1040-SR, Line 38.

Since Turbotax didn't prepare a Form 2210 Part I and Part II, it's not possible to know exactly why a Form 2210 wasn't prepared.  If I prepared the Form 2210 Part I, however, line 6 ( $ 471) would be equal to or more than line 9 ($ -3,530).  The flowchart at the top Form 2210 then states "You don't owe a penalty.  Don't file Form 2210 unless box E in Part II applies, then file page 1 of Form 2210".  Box E in Part II would not apply to my tax returns.

Turbotax could probably be less opaque about the issue by preparing a Form 2210 Part I and Part II and then not sending that document to the IRS in your tax return.  I also understand what the IRS is saying quite clearly ("Don't file Form 2210"), but what real harm is caused by filing a Form 2210 Part I and Part II that would clearly show you don't owe a penalty.