~snip~ but the problem may not be crypto-based gamblers.
You can specify which target market you seek when you advertise on Meta(Facebook, Instagram, etc), which means, any interest or behaviour of the users can be targeted by using keywords like gambling-related and cryptocurrencies-related.
Advertisement on Google and Facebook are very effective way to communicate and reach out to vast majority of gamblers. I hope there is no policy which restricts gambling ads on Facebook.
As has been addressed, you can make an ad about gambling on Meta platforms, but it requires written permission from them and surely it solely depends on each countries regulations. It also applies to Google[1].
[1]
https://support.google.com/adspolicy/answer/6018017