I actually also purchased an EcoFlow River 3 Plus and saw the PR that it was merged into NUT master.
I chose "preview (latest build)" in the backend switch. However, I can't tell from the version (nut-2.8.2-x86_64-7master.ssl31) about when it was actually refreshed or installed.
Is there a way to refresh how this preview build is chosen, so we can get the latest master build of NUT and get EcoFlow support?