The Form 1040 and the Form 1040-SR are exactly the same form.
The Form 1040-SR has a larger typeface and is used by seniors 65 years of age or older. There is no difference between the two forms.
The 1040SR is new starting in 2019. It is the same as the regular 1040 just larger type and the Standard Deduction chart is added to page 1. But has the same line numbers. You automatically get the SR if you or your spouse are 65. If you are using the Desktop program there is a way to force the one you want.
Even the regular 2019 1040 return is now different than 2018. They changed the line numbers again and reduced the new schedules from 6 to 3.
If you use the Desktop program you can switch to forms and the Info Wks part II has a selection to select 1040SR or not. You can not change it in the Online versions. In the Online version if you want to use the regular 1040 form, you can print out the 1040SR and copy the amounts onto the 1040 and then mail your return.
This is the dumbest thing the IRS has done to date ... what they should have done is given the 1040 larger font and 86 the 1040SR form. It is not needed at all ... in fact my professional program allows us to force the 1040 at all times AND has it the larger font on it.
Ok ... so the fools in Congress should be shot ... and the IRS should have talked them out of it. Both are to blame IMO. To bring a new useless form into the works at the same time they majorly reconfigured the 1040 form (twice in two tax years back to back no less) is the definition of insanity.