This question maybe a little tiny.
Firstly, let's input underscript Ctrl+4 in an inline cell.
InlineFormula inline cell $\underset{n\to\infty}{\text{li}}$
However, if we use $\lim$, we get $\lim_{n\to \infty }$ .
Note: it looks the same in my Notebook as Subscript by Ctrl+- $\lim _{n\to \infty }$
TextStyleCell with InlineFormula Inline cells:
For clarity, here's the Cell expression:
cellExpression = Cell[ TextData[{ "subscript: ", Cell[BoxData[SubscriptBox["lim",RowBox[{"n","->","\[Infinity]"}]]],"InlineFormula"], " underscript: ", Cell[BoxData[UnderscriptBox["lim",RowBox[{"n","->","\[Infinity]"}]]],"InlineFormula"] }], "Text" ]; and this is what it looks like in my notebook:
CellPrint[cellExpression] So how to show $\underset{n\to\infty}{\text{lim}}$ in Notebook's InlineFormula cell?
Further, you'll see that when exported to TeX, they are same.
StringCases[ ExportString[cellExpression,"TeX"], "\\begin{document}"~~x__~~"\\end{document}" :> StringTrim@x ] (* {subscript: \(\lim _{n\text{-$>$}\infty }\) underscript: \(\lim_{n\text{-$>$}\infty }\)} *) 




