SolidGrue

For the F-droid enabled users, it seems there’s a Syncthing app in the Termux repos:

~ $ apt show syncthing
Package: syncthing
Version: 1.28.0
Maintainer: @termux
Installed-Size: 26.4 MB
Homepage: https://syncthing.net/
Download-Size: 7857 kB
APT-Sources: https://packages.termux.dev/apt/termux-main stable/main aarch64 Packages
Description: Decentralized file synchronization