Actually the important part is that it's written in red ink, the diagonal angle is meaningless on its own. You would know this if you had read the Magna Carta instead of just watching a YouTube video of someone summarizing it.

A lot of the ideas they have don't seem to have any reason for them, like the diagonal writing and red thumbprint. They're just a loosely associated group of weirdos doing this via word of mouth so it's hard to pin down the reasons for everything.

Seems also like writing the total amount underneath the "Amount Enclosed" box instead of inside it is supposed to mean something special.

My best guess is that official stamps are often at an angle. Of course it is not magic, it is just the stamping person not caring too much about right angles.