Several Months ago, I purchased an ULTRA from "Roku" on Amazon.
I have FOUR issues:
1) Turn off "1 touch play": Settings/System/Control other devices
2) https://support.roku.com/article/208754908
Supported media file types
Different Roku devices support different formats. Newer firmware may support additional formats. The type of audio formats supported is dependent on the type of TV or A/V receiver your Roku device is connected to. Formats supported by your Roku device can be viewed by accessing the ?/Help pages from the Media Device and the Media Type selection screens.
The following file formats are supported:
The following media formats are supported on Roku devices that support 4K
The following media formats are supported on Roku TVs and some Roku players
Notes:
3) Known issue, there are some solutions/workarounds, depending. You can also use an IR-only universal remote.
4) Yes, you should - if you have a Roku 2020 (model 4800) make sure you put it in "Auto passthrough" mode: Settings/Audio/HDMI - If that doesnt work, try manually configuring it for "PCM-Stereo".
To expand on your #2. The MKV file is a container. It can contain a wide variety of video and audio codecs, as well as caption tracks. It can also contain multiple codecs at the same time. Per @StreamerUser 's response, you can see that Roku devices have limited codec support, and if your file has something different, for example VC-1 video, it won't play. You can check the contents of your media a couple of different ways. There is a program called MediaInfo that provides the content of the file. You can also use a program called FFMPEG, which is a command line program but offered more detailed info on the media.