symbf does not play nice with \hat, \tilde, etc. · Issue #501 · wspr/unicode-math · GitHub
fonts - How can I get bold math symbols? - TeX - LaTeX Stack Exchange
Gro-Tsen on Twitter: "Classic LaTeX: the answer to a question which aught to be trivial (getting bold math!) reveals (https://t.co/1ZLpXve2VU) the existence of about 42 packages to do it, with obscure interactions
The bm package
How to bold text in math mode on Quora - Quora
Different math environments available in LaTeX
fonts - How can I get bold math symbols? - TeX - LaTeX Stack Exchange