When I draw a double line without arrow head, it produces \arrow[r, no head, Rightarrow] but compiling it with latex, I get a double line with head. It looks like the correct option is equal instead of no head, Rightarrow.

ConstantLine was introduced in 2018b:
https://de.mathworks.com/help/matlab/ref/matlab.graphics.chart.decoration.constantline-properties.html

when using for example:
xline(4)
This error appears:
`Error using matlab2tikz>handleAllChildren (line 730)
I don't know how to handle this object: constantline
Error in matlab2tikz>drawAxes (line 880)
[m2t, childrenEnvs] = handleAllChildren(m2

I frequently find myself using tlground instead of ground. This is useful, for instance, when you want a resistor to appear halfway between a node and ground:

\begin{circuitikz}
\draw (0,0) to[R,*-] ++(0,-2) node[tlground]{};
\end{circuitikz}

gives

versus