One of your other recent posts mentions Debian 12/Bookworm, if it’s the same LXC container, it’s likely that Syncthing 1.19.2 is installed from Ubuntu’s repo instead of 2.0.10 from Syncthing’s APT repo (minimum of 1.27.3 is required for the “Stay logged in” checkbox).
Did you also follow the recommendation under the “Distribution Package Preferred Over This Version” section on apt.syncthing.net?