Between my own website and SpaceHey, I use the iframe HTML code all the time. I haven't had any issues with iframes so far and I only use them to link videos or audio from YouTube, so there aren't really any cybersecurity threats I need to worry about there.
I'm also not really worried about mobile friendliness either, as my website is primarily designed and optimized for PC users (as many websites from back in the earlier days of the internet were, plus the purpose of my personal website makes it justifiable for a computer focused design along with SpaceHey, a clone of 2000s MySpace).