This is very similar to what the knots, and celtic, TikZ libraries wer designed to do, except they wer designed to work on paths rather than filled regions. Nevertheless, we can take the ideas of those packages and adapt them to this. It's not pretty code because it uses a few low-level commands, but that could be hidden in a package.
We split the drawing into four pieces and draw them one after the other, clipping each piece against the previous one to create the cut-out effect. The clipping only needs to be done when drawing the paths, not filling.
\documentclass{article}
%\url{https://tex.stackexchange.com/q/570414/86}
\usepackage{tikz}
% spath3 package from https://tex.stackexchange.com/q/32125/86
\usepackage{spath3}
% The intention is that the commands of the spath3 package are used by
% other packages which is why much of the structure doesn't have a
% public interface. This means that we have to use \ExplSyntaxOn
% ... \ExplSyntaxOff.
% reverse clip from https://tex.stackexchange.com/q/12010/86
\tikzset{
reverseclip/.style={
clip even odd rule,
insert path={(current page.north east) --
(current page.south east) --
(current page.south west) --
(current page.north west) --
(current page.north east)}
},
clip even odd rule/.code={%
\pgfseteorule
}
}
\begin{document}
\begin{tikzpicture}[remember picture] % needed for the reverse clip
% define and store the various paths
% "outer" part
\path[save spath=outer,domain=0:pi/2,smooth,samples=200]
plot ({sin(deg(\x))+0.6*sin(deg(-3*\x))}, {cos(deg(\x))+0.6*cos(deg(-3*\x))});
% "inner" part
\path[save spath=inner,domain=0:pi/2,smooth,samples=200]
plot ({1.2*(sin(deg(\x))+0.9*sin(deg(-3*\x)))}, {1.2*(cos(deg(\x))+0.9*cos(deg(-3*\x)))});
% joining line between the parts, for filling
\path[save spath=linejoin] (0,2.28) -- (0,1.6);
% joining the parts with a move, for drawing
\path[save spath=movejoin] (0,2.28) (0,1.6);
\ExplSyntaxOn
% We now construct the paths from their constituent parts.
% Reverse the inner path
\spath_reverse:n {inner}
% Clone it into two new paths, one will be for drawing the other for filling
\spath_gclone:nn {inner} {outline}
\spath_gclone:nn {inner} {fillable}
% The filled path consists of the inner, a line out, then the outer, and it is closed
\spath_append_no_move:nn {fillable} {linejoin}
\spath_append_no_move:nn {fillable} {outer}
\spath_close_path:n {fillable}
% The drawn path is similar except with a move in place of the joining line
\spath_append_no_move:nn {outline} {movejoin}
\spath_append_no_move:nn {outline} {outer}
% Clone the fillable path
\spath_gclone:nn {fillable} {fillableA}
\spath_gclone:nn {fillable} {fillableB}
\spath_gclone:nn {fillable} {fillableC}
\spath_gclone:nn {fillable} {fillableD}
% Rotate the clones
\spath_transform:nnnnnnn {fillableB} {0}{1}{-1}{0}{0}{0}
\spath_transform:nnnnnnn {fillableC} {-1}{0}{0}{-1}{0}{0}
\spath_transform:nnnnnnn {fillableD} {0}{-1}{1}{0}{0}{0}
% Clone the drawable path
\spath_gclone:nn {outline} {outlineA}
\spath_gclone:nn {outline} {outlineB}
\spath_gclone:nn {outline} {outlineC}
\spath_gclone:nn {outline} {outlineD}
% Rotate the clones
\spath_transform:nnnnnnn {outlineB} {0}{1}{-1}{0}{0}{0}
\spath_transform:nnnnnnn {outlineC} {-1}{0}{0}{-1}{0}{0}
\spath_transform:nnnnnnn {outlineD} {0}{-1}{1}{0}{0}{0}
\ExplSyntaxOff
% Fill the fillable paths, drawing them as well to ensure that there aren't gaps
\filldraw[cyan] (2.28,0) [insert spath=fillableA];
\filldraw[cyan] (0,-2.28) [insert spath=fillableB];
\filldraw[cyan] (-2.28,0) [insert spath=fillableC];
\filldraw[cyan] (0,2.28) [insert spath=fillableD];
% Draw the drawing paths, each one clipped against the previous one to create the overlay illusion
\begin{scope}
\clip[overlay, reverseclip] (2.28,0) [insert spath=fillableA];
\draw[ultra thick, line cap=rect] (0,2.28) [insert spath=outlineD];
\end{scope}
\begin{scope}
\clip[overlay, reverseclip] (0,2.28) [insert spath=fillableD];
\draw[ultra thick, line cap=rect] (-2.28,0) [insert spath=outlineC];
\end{scope}
\begin{scope}
\clip[overlay, reverseclip] (-2.28,0) [insert spath=fillableC];
\draw[ultra thick, line cap=rect] (0,-2.28) [insert spath=outlineB];
\end{scope}
\begin{scope}
\clip[overlay, reverseclip] (0,-2.28) [insert spath=fillableB];
\draw[ultra thick, line cap=rect] (2.28,0) [insert spath=outlineA];
\end{scope}
\end{tikzpicture}
\end{document}
