The HEVC decoder was never really finished so it mostly works, but some media files cause issues and give no output. S912 also has no support for DV so you won't get output unless media contains a normal HDR fallback stream; some does, but most of the content from online streaming sources does not (to save bandwidth). It's also hard to comment on what happened without seeing a debug log. In the current codebase playback is what it is until Amlogic get further along with upstreaming.
Analogue output is likely a little under-developed given the focus on HDMI so no real comment on that. This wiki article should get the remote working: https://wiki.libreelec.tv/configuration/…ration-advanced - the generic q200/q201 device-tree files intentionally don't contain preconfigured keymaps so you need to define your own.