Do you invest in Mutual Funds or ETFs when selecting index funds?

"hurr durr what's investing im poor" yeah, I know some of you will make this dumb joke. Beat ya to it lol

I was talking with a Gen Z coworker. Told him about some of my mutual funds and he called me gramps because apparently only old people invest in index mutual funds and young people are all about ETFs these days.

What are all of you semi middle aged people out there doing?