Lower case, as you yourself have written in #0.

The act you are referring to is the Sarbanes-Oxley Act.

A trickier question is whether the "the" should be capitalised.

In einem englischsprachigen Vertragstexten würde ich allerdings the Act großschreiben, um damit kenntlich zu machen, daß es nicht irgendein Gesetz ist, sondern dieses ganz bestimmte. Bei der ersten Verwendung oder in einem eigenen Kapitel Definitionen sollte man das auch so festschreiben.

https://www.parliament.uk/about/how/laws/acts/

usually capitalised, in British practice

Sorry! Again what learned, I think one says on Leo.

Thank you all for replying, unfortunately i am none the wiser though :/

#1 I don't think "the" needs to be capitalized

#2 es ist kein Vertragstext sondern ein Info/Blogtext.

#3 good to know, thank you! I do have a British background so my gut instinct was indeed to go for upper case, but I'm writing for an American-oriented journal, so not quite sure...

From what I gather both options are not wrong, so I'll just go with upper case for now.

re #8:

This native AE speaker says: don't capitalize "act" when referring simply to "the act."

But I am not entirely sure, myself.

re #9: aaarrrgghhhhh!!! lol

It seems there is no globally valid answer to the question.

Perhaps it would be safer after all to go with a lower case "act".

#10: I'm sorry for further confusing the matter. I really am not sure and I think it could reasonably go either way.