What changes have they done to pick which ad could be approved?
This is the link to the update https://support.google.com/adspolicy/answer/10688110

The ads that are not allowed:

• Ads for initial coin offerings like ICO.
  Ad destinations that aggregate or compare issuers of cryptocurrencies or related products

If you read all the changes made, it's basically very vague rules. They are not distinguishing which one is actually allowed which any bitcoin-related ad could be subjected to not being allowed.