kaor all! a simple querry, is an angled tang shoulder stronger than a squared and is this more dificult to produce?

Yes it is stronger. I personally don't think it is any more difficult to produce. An angled shoulder is not always appropriate for every time period. There are other variants as well (rounded shoulders, sloped shoulders, etc.).
Best
Hadrian

When cracks develop in aircraft or bridges, one thing they do is drill a hole at the head of the crack. The larger radius spreads the force over a larger area, keeping the crack from growing.

A 90 degree corner has a very small radius, concentrating the stress at that point. You can still have a 90 degree shoulder if you fillet (fill-it, not fil-ay) the corner on, say a 1/4 or 1.2 inch radius.

The radius concepts are correct. A 90 degree corner has infinite stress theoretically ( in cutting direction tang versus blade moments). You could have a mostly square blade shoulder as long where the shoulder meets the tang there is a radius comparable to the radii you see on "angled shoulders". The nice thing about the assembly of the guard to the blade is that some of a large radius can be concealed within the guard. If you had to forge - "drift" or punch the shoulder recess into that guard, the angled shoulder profile would be easier in my opinion. (I have not tried it yet as I am only starting small blades.)