With the new Gmail Connection feature, it is possible to receive and send Gmail messages directly from Proton Mail. However, a connected Gmail address cannot be selected as the default sending address for new messages.

Please allow connected Gmail accounts to be selected as the default "From" address.

This would make migrating family members and less technical users from Gmail to Proton much easier. They could start using Proton Mail as their only mail app without having to remember to manually select their Gmail address every time they compose a new message.

(if they want, over time they can gradually switch contacts and accounts to their Proton address, making the transition away from Gmail seamless).