>unsequenced side effects on the same scalar object are UB

>6.5.3.3.8 tells us that the evaluations of function arguments are indeterminately sequenced w.r.t. each other.

Read 5.1.2.4.3:

"If A is not sequenced before or after B, then A and B are unsequenced."

"Evaluations A and B are indeterminately sequenced when A is sequenced either before or after B, but it is unspecified which."

With a footnote saying this:

"9)The executions of unsequenced evaluations can interleave. Indeterminately sequenced evaluations cannot interleave, but can be executed in any order."

I.e the standard makes a distinction between "unsequenced" and "indeterminately sequenced". And with no mention of side effects on "indeterminately sequenced" being UB it leads me to conclude that your example is not UB.

Side effects matter, and they are always non-portable/implementation defined/dependent on the hardware.

What printf() actaully does is implementation defined - what does "printing mean", does a console even exist? Maybe a user expects it to show graphical ascii/utf8 glyphs on a LCD display? Well, not every computer has that, so now what?