documentclass[varwidth=10cm, preview]{standalone}
usepackage{amsthm, mathtools}
usepackage{unicode-math}
usepackage{microtype}

defaultfontfeatures{ Scale = MatchUppercase }
setmathfont{Latin Modern Math}
setmathfont[range=QED]{XITS Math}

renewcommandqedsymbol{ensuremathQED}

newtheorem{russ}{Theorem by Bertrand Russell}

begin{document}
begin{flalign*}
  & text{True.} &qedsymbol \
  & A = A        &qedsymbol
end{flalign*}

begin{russ}label{vacuity}
If (1 + 1 = 1), I am the Pope.

begin{proof}
I am one.  The Pope is one.  One and one are one.
Therefore, I and the Pope are one.
end{proof}
end{russ}

end{document}