This is not actually LaTeX, but rather MathJax, which threw me a little of in your other question. The reference documentation on this (lifted from the Obsidian documentation) can be found here.
It got a section on Greek letters which reads as follows (slightly modified to show properly in Obsidian style):
In other words, to separate the latin H from the greek H, you can enclose it in $H$. In my setup it does differ, but it’s not very easy to see which is the greek variant
