You should read the documentation of plot():
All you need is to define cumulative return of the four series in columns.
CumulativeReturn = [
5 4 1 6
14 9 4 16
26 17 14 31
40 34 29 55
61 59 52 80
66 63 53 86
75 68 56 96
87 76 66 111
101 93 81 135
122 118 104 160];
Years = [1990;1993;1996;2000;2003;2006;2010;2013;2016;2020];
PlotHandle = plot (Years, CumulativeReturn);
set (PlotHandle, {'DisplayName'}, {'P1';'P2';'P3';'P4'});
set (PlotHandle, {'LineWidth'}, {2;2;2;2});
xlabel ('Years');
xticks (Years);
ylabel ('Cumulative return');
title ('Cumulative returns of the portfolios');
legend ('Location', 'Northwest');
