It isn't about securely sharing highly sensitive material, but enabling verifiable privacy of typical communications. For example (hypothetically) me discussing cancer with a family member, or financial information, or (in countries where there is government oversight) organizing protests.

If not using a secure end-to-end encryption method such as chat, what do you recommend?

Email providers such as ProtonMail provide the same but in the form of email. Telephone calls are not secure, and neither are text messages.