It’s not S912 SOC but S912-B SOC。
Can it use lastest version COREELEC?
Which dtb file should be choosed?
Have a read in the thread link
Here we all use GT1_709N1 but we don’t want to answer your question. Now seriously, testing CoreELEC is easy, painless and won’t spoil your TV Box, grab a microSD or USB flash memory of at least 8GB, and do it! If it doesn’t work, write again in this forum.