At least Pixel 1 is one of the officially-supported lineageos devices, with very straight-forward installation step. Once google stop supporting it, jumping to lineageos is easy enough to do and will give the device another years of life. Nexus 6, an almost 6 years old device, is still officially supported by lineageos, so Pixel 1 will likely get supported well past 5 years as well (assuming the maintainers are motivated enough to keep working on it).

On the other hand, if you use a less popular device, your option will be much more limited as the device get older.