"4k-SMPTE" is true 4K, which is 4,096 by 2,160. The other resolutions are UHD, which is 3,840 by 2,160 (and often called 4K). Most consumer TV's are 3,840 by 2,160.
https://www.extremetech.com/extreme/174221-no-tv-makers-4k-and-uhd-are-not-the-same-thing
Society of motion picture and television engineers is what the acronym stands for. However, I googled it the first time I saw it on my MiBox and still have no idea about it in practice.
I still have to manually adjust my TV off of this setting to a 4k60 setting for Netflix to register as 4k with my TV FWIW