FWIW, you can plug your iPhone into an external monitor to do a Keynote presentation. You need a USB-C (or Lightning) to HDMI dongle in most cases, but it works fine.

- https://support.apple.com/guide/keynote-iphone/present-on-a-...

I'm always reluctant to do non-standard stuff for presentations. There's enough that can go wrong even with a direct HDMI out. I've done it in a pinch but pretty much always carry a laptop with me when I'm presenting along with local copies of my presentations. I've actually gotten a text in the middle of the night asking me if I can fill in for another speaker who forgot and are in a different country :-)