The frequencies that walkie-talkies use are available for walkie-talkie use. Sure, it might need another antenna, but so do features like mmWave, UWB, and Satellite SOS, and I guarantee a genuine walkie-talkie feature would see more usage than those. iPhones already contain antennas for dozens of bands including 600 MHz. I don't see it being infeasible to add ~465 MHz band support.

Unihertz even makes an Android phone with a DMR UHF transceiver, the Atom XL.

https://www.unihertz.com/products/atom-xl