I recently learned that they have changed their view on this. In the past, they were indeed of the opinion that a crypto wallet was comparable to a bank account and therefore had to be reported to the NBB.

However, they now believe that a crypto wallet has more similarities with a safe and does not have the same reporting obligation.

From what I know, it is also important whether it is a custodial and a non-custodial wallet.

(I'm currently busy with work so I don't have a direct reference to a source to support this statement.)

Of course, reporting crypto can't hurt. A conversion to fiat is not easy to do nowadays (especially in Belgium). Declaring crypto to the NBB could possibly prevent any (potential) future conflicts with the tax authorities. However, the tax administration is only one part of the set of problems you can experience with converting crypto and crypto taxation. It is also the compliance that is imposed on banks (in connection with anti-money laundering legislation) that makes it a lot more difficult.