Hello and welcome to "Killian writes an icon tutorial for the first time since 2010", because I'm still making icons and I wanna teach everyone else how to, too~
Made in Photoshop 2020, but you can probably recreate it in as far back as CS2-ish (since I still use the same sort of techniques I've been using since then, lmao). Not sure how well it translates to other graphics software, sorry! Adobe has me in a death grip.

full tutorial here @
killiansicons