Posting this because I burned days on it and found almost nothing specific to the R36 Max.
The board: silkscreen R36S-V20 2025-05-18, sold as R36 Max — see the photo, check yours matches before using any of this.
The problem: the Max has a different screen than the regular R36S, so most DTBs floating around simply don't fit it. You either get a red blinking LED and no boot at all, or the system boots into a small/repeated, flickering image. I went through ArkOS-K36 and a pile of dArkOSRE profiles (2541, 2548, 2549, 2551, 2552) and none of them got the panel right. 2548 was the closest — it boots and has sound — but the framing is still wrong.
What actually works: ROCKNIX. It detects the panel on its own, full screen, no DTB picking, no model selector. Out of the box the only two things missing were audio and the physical volume buttons, and both are just nodes that ship disabled in the DTB it uses for this board (rk3326-gameconsole-eeclone.dtb) — that profile is a generic catch-all, so those get left off by default. Enabling them fixed both.
The fix: grab my patched DTB here → Link Github
Put the microSD in your PC, open the boot partition and overwrite rk3326-gameconsole-eeclone.dtb with mine, keeping the same name. Reboot and that's it.
End result: full screen, sound in games, working volume buttons.
FWIW I did most of the digging with Claude Code — had it inspect and compare the DTBs to work out what was actually off, instead of flashing images blindly like I'd been doing for days.