Yes, the part before "Second try" didn't work for me as well.
Yes, I used your guide to Load Modules:
sudo modprobe -a binder-linux ashmem-linux (which was the part which was not working above, with the ReDroid procedure/script.
This happened to me only using zen kernel, while it worked using the linux-cacule kernel.
But be careful, in the terminal / docker nothing will show up, apart from the ID of your instance, and in my case a couple of error message that at a quick look on the Internet could be disregarded.
To open the "Android" you should have a VNC client (I use TigerVNC), open it and connect with YourIPaddress:5900
Graphically OK but with a bad standard resolution 720x1280, which can be changed passing additional parameters in the docker command, e.g. redroid.width=XXXX redroid.height=YYYY e.g. after -p 5555:5555
It's really worth studying it.
For a certain period I had to use it with other distros (but it shouldn't change much, you should only be careful with some aspects of brtfs, if insterested just search on the forum).
To give you an example, there was a solution I had to use composed by 6 or 7 modules/systems (a web server, a DB server, etc. etc., all configured to work one with each other). I followed the standard procedure and it took a whole day to compile/install, when I found the docker equivalent just the time to copy and paste a string...