Can I use both SD and microSD card readers at the same time with this adapter?

Yes, you can utilize both the SD and microSD card readers at the same time.

What is the maximum resolution supported by the HDMI port on this adapter?

The maximum resolution supported by the HDMI port is 3840 x 2160p at 30Hz.

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StarTech.com DKT30CHVSCPD USB C Multiport Adapter with HDMI and VGA - Mac / Windows - 3x USB 3.0 - SD / micro SD - PD 3.0 - USB C to USB 3.0 Adapter

Add video output and three USB 3.0 ports plus SD/micro SD card readers and GbE port to your laptop through a single USB-C port
Portable USB C Multiport Adapter for MacBook Pro or Windows USB Type-C laptop lets you connect to a 4K HDMI or VGA monitor
Wraparound cable
Power and charge the USBC adapter and your laptop and power peripherals using your laptop’s USB-C power adapter (PD 3.0 up to 85W)
3x USB 3.0 ports to connect devices and fast-charge your phone / tablet
SD and MicroSD slots