Are there bluetooth keyboards and mice available for an iPhone XR?

You should be able to use a BT keyboard. However, the iPhone offers no support for any kind of mouse. If the application you're using to mirror the whats on your computer supports it, you may be able to use a mouse while in that program. Consult the documentation for the application you're using.

Bluetooth don't have device drivers or has to "support" a device Bluetooth has generic driver interfaces called Bluetooth profiles

https://en.wikipedia.org/wiki/List_of_Bluetooth_profiles

so if a Bluetooth device support the HID profile it "just works" used the mac Bluetooth keyboard, used a Microsoft keyboard used some generic small windows Bluetooth keyboard the size of a matchbox

all worked fine with any ios device I paired it with (it needs to be paired though the documentation of the keyboard should describe how, and the keyboard can't have an active connection to another device at the time)

ios does not have a cursor for a mouse to control though so you can't use a mouse