The 4200 was released in Mar 2013, so it's not likely you've kept the manual that came with your Roku. But I don't believe the information you're wondering about was ever contained in any Roku document that was included with the device.
This web page provides the information you are asking about, although there's one supported format not listed. Roku devices will play videos in the M2TS/TS container. The information is valid for your player, as well as the latest devices. Since your 4200 isn't a 4K player, it doesn't support H.265 video. Also note (listed on the linked page) that if your media has DTS audio, the media must be in the MKV container and you need a supporting AVR to play it. Very few TVs support DTS audio.
Yes, Roku does still support your player, as old as it is. It still receives OS updates, but it's approaching end of life for some providers. Don't expect the providers to continue supporting older players, as they build new versions of their channels that require more power and memory. There's a limit to what older players can support.
Dan
Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution."
If you appreciate my answer, maybe give me a Kudo.
I am not a Roku employee, just another user.
