I tried SimpleX but the VPN kill switch on my phone prevents syncing with my computer.
I use telegram primarily as a note taking app with sync features.
Occasionally I send files to friends, so having easy set up for tech illiterate would be great.
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.