Classic Macintosh software can be created using Retro68.

Documentation Inside Macintosh: https://dev.os9.ca/

PLD archive: https://wiki.pldarchive.co.uk/index.php?title=Category:Macintosh

256 colors on SE/30: https://zigzagjoe.com/30Video.html

Many icons: https://www.marciot.com/mac68k-visual-catalog (from this post https://www.facebook.com/photo/?fbid=27766332316389897)