\documentclass[10pt]{article}

%\usepackage[sfmath]{kpfonts}
\usepackage[math]{iwona}
%\usepackage[math]{kurier}
\usepackage[LGR,T1]{fontenc}
\usepackage[math, math-style=ISO,tabular, scale = 0.85]{inter}
\usepackage[utf8]{inputenc}
\usepackage[protrusion=compatibility, expansion=false, kerning=true]{microtype}
\DisableLigatures[f]{encoding = *, family = * }

\DeclareMathSymbol{\upGamma}{\mathalpha}{newoperators}{"00}
\DeclareMathSymbol{\itGamma}{\mathalpha}{newletters}  {"00}
\DeclareMathSymbol{\upDelta}{\mathalpha}{newoperators}{"01}
\DeclareMathSymbol{\itDelta}{\mathalpha}{newletters}  {"01}

%\usepackage[italic, LGRgreek]{mathastext}
%\usepackage[font=Inter-LF]{lgrmath}

\newcommand{\testtext}{%
	Hello, I'm ``Inter'': Ääöüß 1234567890--O. ¿They offered an efficient final workflow!
	$$f(x) = \left( \frac{\alpha \, a \, x^2}{g\,\gamma\,y} \right) + \left[ \int_{-\infty}^{\infty} 3 \times v \, \mathrm{d}v \right] - I / l.$$\par
	$\alpha\ \beta\ \delta\ \epsilon\ \varepsilon\ \zeta\ \eta\ \theta\ \vartheta\ \iota\ \kappa\ \lambda\ \mu\ \nu\ \xi\ o\ \pi\ \varpi\ \rho\ \varrho\ \sigma\ \varsigma\ \tau\ \upsilon\ \phi\ \varphi\ \chi\ \psi\ \omega$ \par
	%$\Alpha\ \Beta\ \Delta\ \Epsilon\ \Zeta\ \Eta\ \Theta\ \Iota\ \Kappa\ \Lambda\ \Mu\ \Nu\ \Xi\ O\ \Pi\ \Rho\ \Sigma\ \Tau\ \Upsilon\ \Phi\ \Chi\ \Psi\ \Omega$ \par
	$\Delta\ \Theta\ \Lambda\ \Xi\ \Pi\ \Sigma\ \Upsilon\ \Phi\ \Psi\ \Omega$ \par
	{\fontencoding{LGR}\selectfont a b g d e z h j i k l m n x o p r s c t u f q y w.}\par
	{\fontencoding{LGR}\selectfont A B G D E Z H J I K L M N X O P R S T U F Q Y W.}\par
	\bigskip
	$\upDelta x$ $\itDelta$ $\upGamma(n)$ $\upGamma(z)$ $\itGamma$ $a \alpha$, $p \rho$, $u \upsilon$, $v \nu$, $y \gamma$
	\bigskip
}

\begin{document}

\noindent\testtext

\noindent\textit{\testtext}

\boldmath

\noindent\textbf{\testtext}

\noindent\textit{\textbf{\testtext}}

\end{document}