Can I use this adapter to mirror content on two separate monitors?

Yes, the multiport video converter allows you to mirror or extend content on two separate monitors simultaneously.

What is the maximum resolution supported by this USB to HDMI VGA adapter?

The adapter supports HDMI resolutions up to 3840x2160 (4K) at 30Hz and VGA resolutions up to 1920x1080 at 60Hz.

double click image to zoom in

StarTech.com USB32HDVGA USB 3.0 to HDMI VGA Adapter - External 4K 30Hz Video & Graphics Card for Mac & Windows - 2-in-1 Multiport Dongle (USB32HDVGA)

Maximize your laptop’s video compatibility with a 2-in-1 adapter: USB-A to HDMI and VGA
USB 3.0 external graphics & video card supports UHD resolutions up to 4K 30Hz
Boost your productivity by creating a dual screen workstation w/ the USB 3.0 to HDMI VGA multiport adapter
The multi display dongle provides a convenient solution for adding multi monitor capability to your computer
The multiport video converter lets you mirror or extend content on two separate monitors simultaneously