Here's some of the privacy recommendations from the article for when using proton mail:

For users concerned about privacy, particularly those involved in sensitive or political activities, OPSEC should be a top concern when using privacy tools. It’s advisable to:

• Avoid linking recovery emails or phone numbers that can directly tie back to personal identities or primary business activities.
• Consider using secondary, disposable emails or virtual phone numbers that offer an additional layer of anonymity.
• Use a good VPN service to hide your IP address whenever possible. (Failure to do this is what compromised a Proton Mail user in France who was arrested after after police obtained IP logs.)
• Consider purchasing services using an anonymous payment method.
• Stay informed about the legal obligations and policies of communication service providers, especially regarding their compliance with international law enforcement requests.