Noto Sans Tibetan was not actually a sans font. On newer systems the
font is now Noto Serif Tibetan.
See, e.g., the package 'fonts-noto-core' in Ubuntu 21.04.
This change also fixes compilation of
supported-languages_polyglossia-XeTeX.lyx on Ubuntu 21.10.
\newfontfamily\telugufont{Noto Serif Telugu}
\newfontfamily\thaanafont{FreeSerif} % prevent "missing script tag" error
%\newfontfamily\thaanafont{Noto Sans Thaana} % works, too
-\newfontfamily\tibetanfont{Noto Sans Tibetan} % wrong family
+\newfontfamily\tibetanfont{Noto Serif Tibetan}
% Font setup for Japanese (not supported by Polyglossia)
\usepackage{ifxetex}
\newfontfamily\telugufont{Noto Serif Telugu}
\newfontfamily\thaanafont{FreeSerif} % missing script tag in FreeSerif
%\newfontfamily\thaanafont{Noto Sans Thaana} % works, too
-\newfontfamily\tibetanfont{Noto Sans Tibetan}
+\newfontfamily\tibetanfont{Noto Serif Tibetan}
% Font setup for Japanese (not supported by Polyglossia)
\usepackage{ifxetex}