Proton Mail encrypts the content of the mails, not the subject. So even if it is a Proton Mail-to-Proton Mail conversation the subject is not encrypted. Skiff also encrypts the subject of the mail in a Skiff-to-skiff conversation.

I said this in Reddit, I will say it here too.

"Well,

(Note: Most of my family and friends don't really care about privacy.)

So, it’s kiiiiinda about my privacy, since I do NOT feel comfortable using a Meta product.

Because most of my family have FB, FB Messenger, IG and/or (well, of course) WA."

+I want to increase their privacy and security as well.

OpenBoard, Florisboard, AnySoftKeyboard

THERE ARE ALTERNATIVES, PEOPLE!