I'd recommend this as a great time to start building directly from the source (either LOS or AOSP) so you can provide yourself with updates, including Android Security Bulletins, as they are merged in to LOS or AOSP.

You won't get any device-specific updates or bugfixes without applying them yourself (or going out of tree), but someone already did the hard work since it's an official device and has essentially full functionality. You'll be able to keep your device supported until Lineage drops the version.

Curiously, which device did you purchase?