Apple's equation support in Pages, Numbers, and Keynote is restricted to the subset of LaTeX/MathML syntax that is supported by the inherent translator in Pages. You can read more about that support, and the syntax restrictions in the following article, and by downloading the blahtex user guide (PDF) that describes the allowed syntax:
About LaTeX and MathML support in Pages, Numbers, and Keynote - Apple Support
See also: What’s the last Mac OS that supported Pag… - Apple Community
If you want to input Unicode, you can launch the Emoji & Symbols (Character viewer) panel and double-click a character to insert it where the x appears in:
\textrm{x}
\textrm{⌘}
The blahtex manual mentioned above has a large table of LaTeX symbols that are supported too. You can also directly enter MathML as blahtex would convert any LaTeX input to embedded MathML in Pages. This equation survives opening an exported Word (docx) in MS Word (e.g. Office 2021 for Mac) too.