Is there a way to change this threshold?
No.
Force labeling?
Yes.
D = digraph(sprand(150, 150, 0.1));
h = plot(D); % No labels
figure
h = plot(D);
h.NodeLabelMode = 'auto';
Or if you want to label only a few nodes see the labelnode function.
figure
h = plot(D);
nodesToLabel = 1:30:numnodes(D);
labelnode(h, nodesToLabel, string(nodesToLabel))
