How can I mirror one laptop presentation on two venue TVs?

The most reliable solution is an HDMI splitter or, preferably in a venue, an HDMI distribution system. Connect the laptop to the splitter and send the same output to both TVs. If the TVs are far away or already connected to other equipment, you may need an HDMI-over-CAT or wireless HDMI receiver for the second display. Standard casting usually behaves as a separate display and may not mirror consistently with a wired HDMI connection.

On Windows, connect the HDMI cable and press Windows + P. Choose Duplicate rather than Extend or Second screen only. If Windows reports three displays, open Settings > System > Display, select each detected screen, and check which physical TV it represents. You can also choose the laptop display and one TV, then duplicate those, but Windows may not support duplicating the same output across a wired display and a cast receiver.

The wall HDMI plate is probably just a pass-through cable to one input on the venue’s AV system; it doesn’t automatically distribute the signal to both TVs. Both TVs may also be connected to a hidden switcher or splitter. Once the laptop is visible on one TV, check every input on the second TV and confirm the venue equipment is routing the same HDMI source there.

If the laptop has a USB-C port that supports video output, a USB-C-to-HDMI adapter could provide another wired video output. However, that still requires two available inputs or an appropriate AV distribution device. For a presentation, two wired outputs are generally more dependable than combining HDMI with wireless casting.