i have a usb c to HDMI dongle , a mi9 phone and non smart tv , can i screen miror my phone to the tv ....my dad has note 9 and he can connect his phone by samsung Dex but i can not run it on my phone so what should i do ?
You have to check with Xiami' support whether there is support for HDMI-over-USB for your phone. If there's, you will probably need new dongle as well.
See XDA Developers for hacks, if any.