Proton’s statement from the linked article

“We are aware of the Spanish terrorism case involving alleged threats to the King of Spain, but as a general rule, we do not comment on specific cases. Proton has minimal user information, as illustrated by the fact that in this case, data obtained from Apple was used to identify the terrorism suspect. Proton provides privacy by default and not anonymity by default because anonymity requires certain user actions to ensure proper OPSEC, such as not adding your Apple account as an optional recovery method.”