I saw this news today and went to find out if it was true or not, after all it is a bit strange that he would bet and lose 1 million that easy.
I know Neymar likes to play poker, and he probably plays with high values, but in this case it wasn't making much sense.

I found a source, but it is in Portuguese, that says that everything was just a marketing move, and the value probably wasn't Neymar's, so there was no investment on his part and no loss of money.
Source here: https://ge.globo.com/blogs/brasil-mundial-fc/post/2023/03/29/neymar-chora-ao-perder-1-milhao-de-euros-em-poquer-assista.ghtml

The funny thing in the end is that the marketing works, after all there are a lot of people commenting on this news today, and even here we are talking about hehehe.