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fontspec all the fonts!
A sampler of the OTF/TTF fonts installed on Overleaf that you can use with fontspec in XeLaTeX and LuaLaTeX, including for various scripts/languages.
Overleaf
Using Open XITS Fonts with XeLaTeX
The XITS fonts provide a Times-like serif typeface for mathematical and scientific publishing. They provide a version of the STIX fonts enriched with the OpenType MATH extension, making them suitable for high quality mathematical typesetting with XeTeX and LuaTeX. XITS fonts are free and open source.
Overleaf