There are different kinds of ligature systems. As of writing this answer:

Material Icons uses: LIGA

Material symbols uses: RLIG

WPF does not support RLIG ligatures.

Here is an article with further detailed explanations:

https://reviewpoint.org/blog/liga-and-rlig

Here is an issue that I opened in the Material Icons Repo. The dev was very friendly and they consider adding the support for RLIG in the future. It also contains further explanations and a hint to convert a font from RLIG to LIGA.

https://github.com/google/material-design-icons/issues/1891#issuecomment-2905094093