I think VS Code is one of the best editor/IDE for Inform 6 right now. (Disclaimer: I actually don’t code in I6 that much, and I’m the maintainer of the VS Code Inform 6 extension.)
Regarding VS Code, there’s the inf6langtools extension that adds an object/class tree to navigate the code. In my very limited experience of it, it might mark some valid code as errors, but I suppose it depends on the project.
In case you haven’t seen it, there’s also the IF Player extension that allows to open and play Z-machine and Glulx files directly in VS Code.
I am currently writing a Punyinform game for Punyjam 1. vscode with the Inform 6 extension has very good source code highlighting. When I am in Win 10, I just keep a terminal window open and compile the code there. It literally takes less than a second to compile then go back to vscode even on my modest computer. I also keep a window with Gargoyle open to test the z-file. Probably easier then setting up the IDE.
I generally use vim on an RPi in a terminal interface. Vim does a pretty good job with source code highlight as well. You can use Genie and/or vscode in a GUI on the RPi as well. I just do better with a text terminal.
I’m using Atom to code Inform 6 on Windows 10/64bit, I’m able to build and run the game directly from the editor and zoom directly to lines with compilation warnings and errors. Getting that working took a little effort, if you decide to try it feel free to ping me, I’ll share my atom-build.yml file (that specifies the paths for how to build, and the regex for parsing the warning and error messages)