a VS code extension for writing assembler, C, Pascal, or something else that compiles to 6502 would be nice, but I haven't found one for THOSE, yet. However, for BASIC, there some other options for developing for the Apple II.
Funny you should mention Visual Studio Code, I just found this yesterday:
https://marketplace.visualstudio.com/items?itemName=dfgordon.vscode-language-applesoft
It even has mouseover info for pokes and peeks that tell about the address you are working with.
It doesn't seem to be complete yet, but it was updated May 2022, so I think the author may still be actively developing it.
In my earlier searches for modern ways to develop for the apple II, I came across this:
https://virtualbasic.org/
I was thinking about contacting the author of the vs code extension and asking him about implementing some of the features of virtual basic into it.
Virtual BASIC lets you code Applesoft BASIC (and Integer BASIC maybe?) with modern indenting style, and it has the ability to separately label and define gosub routines. The labels for gosub routines require using the british pound symbol though, but I looked at the code and it's easy to substitute that to something else.
After you've finished coding, it can convert the code you've written into properly numbered BASIC statements, which you can then save to a text file then do something like SHIFT+INSERT into Applewin or whatever.
Please note Virtual BASIC requires Python 2, but as a result, it is cross platform. It hasn't been updated since October of 2019.
I'm currently "disassembling" some of my old favorite Apple II games that were written using BASIC (+ some ASM,) to get the logic written out so I can re-implement for modern platforms (with my own ideas for additions / corrections.)
I haven't looked at CC65 yet, but that seems like something that might be useful as well.
There doesn't seem to be any all-in-one tool that lets you write for, compile, and debug for the Apple II in both high-level languages AND assembly at the same time, and/or disassemble those types of things (unless you count the Applewin debugger, which as GREAT as it is, isn't documented very well.)
As near as I can see the closest thing to a somewhat complete package for Apple II development on modern platforms seems to be the 8-bit Unity, but I haven't looked at it yet.
Just a note, as I was about to hit the submit reply button I also found THIS:
https://www.howtogeek.com/809799/45-years-later-the-apple-ii-still-has-lessons-to-teach-us/