Hello everyone! Long time no update but I figured I'd let the community know in case this helps anyone else.
If anyone wants a working version of the setup script, I have scripts that will compile the latest nightly:
http://www.trinitymugen.net/~Creator/Jesuszilla/scriptmodules/ports/ikemen-go-nightly.sh
http://www.trinitymugen.net/~Creator/Jesuszilla/scriptmodules/supplementary/golang-1.20.sh
Replace the scripts in the setup steps with these if you want a working version of the latest nightly installed separately. @SuperFromND should be working on new scripts in the future but this will allow you to install a separate nightly build for now (which includes 3D stages but beware: they don't perform well on Pi 4 as of the date of this writing; someone is working on improving the 3D rendering as I write this post).
A user in the I.K.E.M.E.N Discord confirmed these modified scripts work with Pi 5 as well and 3D stages do perform better there from what I've seen from footage (I have no Pi 5 to test myself but the confirmation is good).
EDIT: If replacing the steps in the tutorial above with my scripts, make sure to surround the URL's in quotes " " like so:
sudo wget "http://www.trinitymugen.net/~Creator/Jesuszilla/scriptmodules/ports/ikemen-go-nightly.sh"
~ Is a special character in shells so that could cause errors trying to use the command otherwise.