Again, you are assuming that Lauda lives in Croatia.
For some reason I'm thinking that Lauda doesn't live in Croatia, unless he/she/it/we/you/they is a transplant from another country that has English as its first language--or Lauda has somehow acquired the writing skills that we've seen. Could be. I've been fooled before by people even when they're standing right in front of me.
But as far as whether law enforcement would care about the "extortion". The entire scope of that operation was a few PMs or e-mails related to a bitcoin discussion forum, with a plausable purpose other than extortion, which was never followed through on, and which presumably was never reported to law enforcement. Yeah, I don't think the FBI or any other government agency is going to be jumping all over that. They tend to go after much bigger fish and only when there's strong evidence that a crime occurred. Again I could be wrong, but I don't think this or any tax evasion prosecution is much of a possibility.
I'd also like to remind Quickseller here that
I'm not Lauda. I never did see him come through on that bet he was supposed to place that he had enough evidence of that to convince a disinterested 3rd party.