Use -smooth to draw curved arrows. You just have to provide more points. If the middle points are slightly different, the lines will bend in a non overlapping way:

my $id1 = $canvas->createLine(60, 60, 220, 240, 400, 400,
                              -smooth => 1,
                              -arrow => "first",
                              -arrowshape => [ 20, 20, 20]);
my $id2 = $canvas->createLine(60, 60, 220, 260, 400, 400,
                              -smooth => 1,
                              -arrow => "last",
                              -arrowshape => [ 20, 20, 20]);
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