I know that habit of using messenger app for notes :) Try [matrix] using Element or SchildiChat. It's e2eencrypted and federated, and even supports markdown formatting in messages. Also some Slack features are included. The only issue for non-techy person might be verifying sessions - just be sure to use the same client on all devices.
I know that habit of using messenger app for notes :) Try [matrix] using Element or SchildiChat. It's e2eencrypted and federated, and even supports markdown formatting in messages. Also some Slack features are included. The only issue for non-techy person might be verifying sessions - just be sure to use the same client on all devices.