So I guess the untrusted client is outdated. But I followed the exact instructions from https://apt.syncthing.net. Therefore using apt update && apt upgrade syncthing doesn’t do anything:
sudo apt upgrade syncthing
Reading package lists... Done
Building dependency tree... Done
Reading state information... Done
syncthing is already the newest version (1.12.1~ds1-4).
Further down on the same installation webpage is a section about setting the priority. Without doing that, the version in the default repo for your Debian or other Debian-based Linux distribution takes precedence (i.e., you have two version of Syncthing available when using the command apt install syncthing)
Use the following command to see details about the default package:
Oh oups I skipped that section in my head. But now how do I upgrade my existing installation? I typed the command given in the documentation, but it still doesn’t let me upgrade anything.
Nevermind I fixed it. Had to manually add **echo "deb [signed-by=/usr/share/keyrings/syncthing-archive-keyring.gpg] https://apt.syncthing.net/ syncthing stable" | sudo tee /etc/apt/sources.list.d/syncthing.list* again for some reason, but now it updated successfully. Thanks for all your help!