Making 500K euros in 6 months; myth or plausible?

While it's technically possible, I wouldn't bet on it. Lots of people have launched startups that were a sure thing just to have them fail with no users. If you need money I would get a job.

Edit: if you need some demotivational material, you can check out https://www.failsights.com. A guy I know in the UK does it, and he covers startups that fail, often costing the founder significant amounts of money

Its happening with AI wrappers (eg. AI headshot) and smart-contracts; but it will ~probably~ take more than 6-months to familiarize yourself with the space and market; if you had the domain knowledge, you could succeed insofar as there is not much code to write.

If it was easy, everyone would do it

Depends on how big the initial investment is. If you start with 1000 euros - unlikely. If you start with 5,000,000 euros - plausible. Large scale marketing costs heaps and returns only a tiny percentage of paying customers.

In a six month period some time in the future? Plausible.

In the next six months? Unlikely enough to be a myth.

No joke, I'm aiming for at least 5 million in next 8-9 months, AMA :) I'm serious

Completely plausible: invest 17M EUR in dutch or belgian 6 month bonds