\documentclass[crop,tikz]{standalone}% 'crop' is the default for v1.0, before it was 'preview'
\usepackage{fontawesome5}
\usepackage{tikz} % TeX Plots
\usetikzlibrary{shapes.symbols, fit}
\definecolor{HUBlue}{RGB}{0,55,108} % HU colors
\definecolor{HUSand}{RGB}{210,192,103}
\definecolor{HULightBlue}{RGB}{116,151,197} 
\definecolor{HULightGray}{RGB}{230,230,225}
\definecolor{HUBlack}{RGB}{10,10,25}

\begin{document}
{\fontfamily{cmss}\selectfont
\begin{tikzpicture}[node distance=2cm,every node/.style={scale=.9},
pers_teach/.style = {rectangle, draw=HUBlack, line width=.7pt, minimum width=1.8cm, text width=2.2cm, minimum height=1.3cm,text centered, fill=HUBlue!50},
onl_teach/.style = {rectangle, draw=HUBlack, line width=.7pt, minimum width=1.8cm, text width=2.2cm, minimum height=1.3cm,text centered, rounded corners, fill=HUBlue!10},
pers_class/.style = {rectangle, draw=HUBlack, line width=.7pt, minimum width=1.8cm, text width=2.2cm, minimum height=1.3cm,text centered, fill=HUSand!50},
onl_class/.style = {rectangle, draw=HUBlack, line width=.7pt, minimum width=1.8cm, text width=2.2cm, minimum height=1.3cm,text centered, rounded corners, fill=HUSand!10},
]
        % Add or remove the ", draw = orange, line width=1.2pt" in the brackets from a node to add or remove the orange border
    	\node(INT) [onl_teach, draw = orange, line width=1.2pt] {\faUsers~~\faPhone\\Onboarding\\kw 8};
    	\node(CO1) [onl_teach, right of = INT, text width = 1.8cm, xshift = -.5cm, yshift = -1.8cm] {\faUser~~\faPhone\\Support 1};
        \node(CO1_anch)[right of = INT, xshift = -.5cm, yshift=.1cm]{};
        \node(DLET) [onl_teach, right of = INT, text width = 1.8cm, xshift = 1cm] {\faUser~~\faLaptop\\Handbuch\\ };
    	\node(M1) [pers_teach, right of = DLET, xshift = 1cm] {\faUsers~~\faUniversity\\1. Treffen\\kw 10};
    	\node(M2) [pers_teach, right of = M1, xshift = 1 cm] {\faUsers~~\faUniversity\\2. Treffen\\kw 11};
        \node(CO2) [onl_teach, right of = M2, text width = 1.8cm, xshift = -.5cm, yshift = -1.8cm] {\faUser~~\faPhone\\Support 2};
        \node(CO2_anch)[right of = M2, xshift = -.5cm, yshift=.1cm]{};
    	\node(DLE) [onl_class, right of = M2, text width = 3.8cm, xshift = -.5cm, yshift = 1.6cm] {\faUser~~\faLaptop~~\faPlus~~ \faUsers~~\faLaptop\\~~DLE~~~~~~~~WebApp};
    	\node(T) [pers_class, right of = M2, xshift = 2 cm, text width=3.5cm, rounded corners] {\faChalkboardTeacher\\Eigener Unterricht\\kw 12 -- 19};
    	\path (T.west) -- (T.north west) coordinate[pos=0.5] (T1);
    	\node(M3) [pers_teach, right of = T, xshift = 1.8 cm] {\faUsers~~\faUniversity\\3. Treffen\\kw 20};
    	% \node(CO3) [onl_teach, text width = 1.8cm, right of = M3, xshift = 1.5 cm] {\faUser~~\faPhone\\Debrief\\kw2+};
    			\draw[->, line width=.7pt] (INT) -- (DLET);
    			\draw[->, line width=.7pt] (CO1) -- (CO1_anch);
    			\draw[->, line width=.7pt] (DLET) -- (M1);
    			\draw[->, line width=.7pt] (M1) -- (M2);
    			\draw[->, line width=.7pt] (M2) -- (T);
    			\draw[->, line width=.7pt] (CO2) -- (CO2_anch);
    			\draw[->, line width=.7pt] (DLE) |- (T1);
    			% \draw[->] (T) -- (M3);
    			\draw[->, line width=.7pt] (T) -- (M3) node[midway, yshift = .3cm]{};
\end{tikzpicture}
}
\end{document}