The 2nd and 3rd answer provide the symbol that you are looking for, combined with a subscript \infty.
– MarijnMay 25 '22 at 18:30
See also https://tex.stackexchange.com/questions/212050/looking-for-stylized-h-symbol, https://tex.stackexchange.com/questions/625553/special-symbol-of-h.
– MarijnMay 25 '22 at 18:33
\infty. – Marijn May 25 '22 at 18:30