It is possible to draw 2D line in edit mode

Development Asset Creation
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DrawDebugHelpers.h what you are looking for. It has a few useful global functions.

// FlushPersistentDebugLines(GetWorld());
const FVector A = FVector(0.0f, 0.0f, 0.0f);
const FVector B = FVector(100.0f, 0.0f, 0.0f);
const FVector C = FVector(100.0f, 50.0f, 0.0f);
const FVector D = FVector(0.0f, 50.0f, 0.0f);
DrawDebugLine(GetWorld(), A, B, FColor::Purple, true, -1, 0, 5);
DrawDebugLine(GetWorld(), B, C, FColor::Purple, true, -1, 0, 5);
DrawDebugLine(GetWorld(), C, D, FColor::Purple, true, -1, 0, 5);
DrawDebugLine(GetWorld(), D, A, FColor::Purple, true, -1, 0, 5);