There are newer devices that can use LineageOS right away, such as Huawei’s P20 Pro, Samsung’s 2016-era Galaxy Tab S2 tablets and Xiaomi’s Pocophone F1. Wider support is on the way, Lineage added, and there’s even a bit of future-proofing: hooks in LineageOS should make it compatible with Android’s expected dark mode.
As always, you have to be willing to install unofficial code. This isn’t for people who absolutely need a reliable phone for work. If you’re comfortable with a bit of tinkering, though, this could help you postpone a hardware upgrade for another year or two.