Erd\H{o}s produces the following symbol instead of the slanted accent over o.
Note: it is not typical latex output. Fontspec was used to change font and weight. Here is the code. I am currently using Erd"{o}s which produces a vertical accent instead of the slanted one. The output I would like is 
\documentclass{article}
\usepackage[T1]{fontenc}
%\usepackage{lmodern}
\usepackage[no-math]{fontspec}
\setmainfont{ModernMTStd-Extended.otf}[
FakeBold=2,
%SmallCapsFont=MrsEavesSmallCaps_Regular.ttf,
%BoldFont=Monotype-Modern-Std-Bold_31159.ttf,
ItalicFont=ModernMT-ExtendedItalic.otf,
BoldItalicFont=ModernMT-ExtendedItalic.otf,
Ligatures=TeX,
]
\setsansfont[%
FakeBold=2,
ItalicFont=NewCMSans10-Oblique.otf,%
BoldFont=NewCMSans10-Bold.otf,%
BoldItalicFont=NewCMSans10-BoldOblique.otf,%
SmallCapsFeatures={Numbers=OldStyle}]{NewCMSans10-Regular.otf}
\setmonofont[%
FakeBold=2,
ItalicFont=NewCMMono10-Italic.otf,%
BoldFont=NewCMMono10-Bold.otf,%
BoldItalicFont=NewCMMono10-BoldOblique.otf,%
SmallCapsFeatures={Numbers=OldStyle}]{NewCMMono10-Regular.otf}
%\let\mathbbalt\mathbb
\usepackage{unicode-math}
\setmathfont{NewCMMath-Book.otf}[FakeBold=2]
%\let\mathbb\mathbbalt
\begin{document}
Erd\H{o}s
\end{document}
\H{z}work? if not the question is essentially a duplicate of the automatically linked question https://tex.stackexchange.com/questions/49313/poor-mans-double-acute-accent?rq=1 – David Carlisle Aug 06 '21 at 13:18\H{z}– David Carlisle Aug 06 '21 at 14:02fontencbe messing with that? – campa Aug 06 '21 at 14:06\usepackage[T1]{fontenc}never use that with lualatex or xelatex. (although as you load fontspec afterwards fontspec will corect this error it will not do any harm in this case.) – David Carlisle Aug 06 '21 at 14:08fontencandlmodern– Masum Aug 06 '21 at 14:09\rmfamilyinside \H. this is very weird that the other solutions do not work in this case. Thank you very much @DavidCarlisle – Masum Aug 06 '21 at 14:13