Just Orange Pi brand has like 30 different boards. And Linux kernel has 6 different LTS versions, stable version, and master branch. If you want to ask about mainline support, you can pick the board and just go to whichever Linux kernel version you intend to be using, and check for yourself.
Corresponding dts file will be in either one of these directories for 95% of Orange Pi boards (the rest that don't use Rockchip or Allwinner SoCs are better ignored):
Corresponding dts file will be in either one of these directories for 95% of Orange Pi boards (the rest that don't use Rockchip or Allwinner SoCs are better ignored):
https://elixir.bootlin.com/linux/latest/source/arch/arm/boot...
https://elixir.bootlin.com/linux/latest/source/arch/arm64/bo...
https://elixir.bootlin.com/linux/latest/source/arch/arm64/bo...