Recipients with Thunderbird see your files as natural email attachments, others can access them securely via a link.

From: https://www.tb.pro/en-US/send/

https://proton.me/wallet

If your distro offers it, rootless podman + podman system service is the best setup, IMO. That will give you a docker command that is 1-to-1 compatible with docker and lets you use tools like docker-compose that expect a docker service socket. Then you can just follow tutorials that only explain things for docker.