I am not an expert on security and I don’t know how to setup ddns, but I simply use Tailscale VPN to access my RPi4 homeserver running Umbrel from outside of my home, I simply installed Tailscale in my Umbrel and in my phone, and when I want to access from my phone Immich, Nextcloud or any other app running on my Umbrel. I simply enable the Tailscale VPN. Maybe it has some limitations, but is the simpler way I found, and based on what I read, it is more secure than exposing a port in the router, but not sure.

Umbrel OS

I use Logseq in my PC and my phone and I unse Syncthing to sync the notes accross my devices.

I really hope so, it should be taught, because for me it was a slow learning process. First I started using Obsidian, and moving all my notes from Evernote, Notion, and others manually. After that I moved to Logseq, which is like Obsidian but open-source. And the last step was using an open-source syncing tool (Syncthing) to have my notes synced locally in all devices. And now I have been 2 years self-hosting my notes in a really easy way.