raspbian is old 32-bit ARMv6, or maybe you use wrong naming. I see orangepi pc2 is also 1GB RAM and 4x Cortex-A53. So that is the same as RPi3B+. Armbian should be 64-bit on the orangepi pc2 and if that runs fine for you with HA, then it should also run fine the same way on RPi3B+. Armbian has no 32-bit support for raspberries, so maybe have a look if there is a ready-made image. The root filesystem on the orangepi pc2 you have currently should run almost unmodified on a RPi3B+. The issue is that raspberries boot filesystem is proprietary, but if you know or get to know how it works, you could get it to run.

That might be due to little RAM. I did a test install about a year ago on a raspi 3b+ with 1GB RAM, and it became extremely slow after a short while. htop showed, that the system was completely busy with swapfile access. Even a shutdown took some hours. Homeassistant might claim, that 1GB can suffice, but IMO that's more a proof-of-concept than a workable solution. As soon as you add some integrations, the free memory becomes quickly too low.

Maybe I am misunderstanding your question but: Armbian is one operating system, and Guix system is another operating system, so no. It's the equivalent of asking "can I install debian but boot NixOS from debian on another storage device". Unless it's a virtual machine you are talking about, you might be able to run a Guix system as a virtual machine in armian, but I don't think that is what you are asking. If you want to run Guix system, you need to boot Guix system. If it's just the package manager Guix you are talking about, then afaik also no (if you are talking about the guile scheme), for that to work you need to run Guix system, just like you need to use NixOS to run nix package manager. But I could be incorrect.

I have also tried to build a new image and I am now getting a new error related to 16kb size. I have previosly had success 26.2.0 trunk 151, which was able to boot and worked quite well, Excluding known issues such as HDMI support and Fan speed needing to be adjusted with a script. Issue is that this build is no longer available. I think until we get more demand from Retroid Community we might just be out of luck

Is it possible to run armbian with pre-installed homeassistant on a raspberrypi 3B+ ? The reason of my question is, I have running homeassistant on a orangepi pc2 which work very well. On the raspberrypi 3B+ running unter raspbian, homeassistant is very slow.