Re: Horsecrap - MyffyW
1st party = Nexus or Google Pixel
2nd party = Samsung, LG, Huawei, etc devices on an OTA upgrade path from the OEM
3rd party = a customised version of 2 sold to you by a carrier, with special uninstallable carrier apps skins bootup logos etc.
Sorry, but I'd place the Google/Nexus devices in "2nd party" as well, considering their inability to keep up on updates as well.
The only thing that would qualify as "1st party" would be anything that can be readily flashed with the latest LineageOS build. If you can't fully control the device, you don't really "own" it, regardless of how much you paid for it.