Zarlin

No full guarantee, but scanning all downloaded files using a tool such as malwarebytes can help catch a lot of malware.

And ofc the most important one: Common Sense! If something seems too good to be true, it probably is.

Obsidian + Syncthing has been working prefectly for several years now for me, across Windows, Android and Linux.

The systemd website itself seems quite information-rich: https://systemd.io/

This is the currently maintained android version: https://github.com/researchxxl/syncthing-android

Take a look at Bunny ( https://bunny.net/dns/ ), they’re based in Europe with worldwide coverage, and have a lot of other useful services as well.