Can I use a USB mixer in place of a USB interface and perform a multitrack recording?
That depends on what mixer are you using. Better said, what is getting out to USB interface. On cheaper mixers you can get only master out, on bit more expensive you should be able to get all of the channels. Check the specifications of your mixer.
Like @Saba mentions it is totally possible but it all depends what type of mixer you have.
Make sure to check the spec carefully as many mixing desks come with multiple channels but only have one master mix out via USB to your computer.
Careful to also look for USB ≥ 2.0 or even better Thunderbolt if you’re on macOS.
I searched carefully and the best multitrack mixer (that allows every channel to be mapped on your computer to any DAW) is the Soundcraft Signature 12 MTK.
Is the mixer capable of having it’s audio interface updated with new drivers or firmware?
They do have a driver on the downloads section of the Soundcraft product page. It appears to be Windows only for Mac my experience has been plug and play.