I have used HikingProject for years, all over the US. It's great for finding trails, seeing photos of them, reading descriptions, and so on. It's been a huge help to planning many vacations.
There is one "but."
In my experience HikingProject consistently under-reports trail distances, often significantly. This week, for example, a hike in the Grand Canyon that HikingProject lists as 2.9 miles registered as 4.1 as-hiked for me with a GPS tracker, and a hike in Sedona that HikingProject lists as 5.4 miles registered as a 7.8 as-hiked for me with a GPS tracker.
Those may not seem like big differences, and in absolute terms maybe they're not. But they're each off by more than 40%.
These two examples were not a problem for me, but if you're hiking a challenging trail on the edge of your experience level, or hiking in bad weather, or fighting darkness, the trail turning out to be 40% long than expected is bad, bad news, and a legitimate safety issue. Forty extra percent turns a ten-mile hike into a 14-mile hike, and a 20-mile hike into a 28-mile hike.
My advice: use HikingProject, but build in a significant buffer on the distance.