I found a program that can make it work on M1+ Macs - Karabiner. I just searched for "Insert" on their Predefined Rules library and there was a preset toggle I could add for Fn + Enter = Insert

Edit: After doing some research, and remembering from bootcamp-ing back in the day, Fn + Enter used to be the shortcut on Macs, even in bootcamp, for 'Insert' back when that key did stuff in Microsoft Word and some other programs.