HDMI audio not detected

I'm on Ubuntu 20.04.3 LTS, on a thinkpad T480. I just bought a new TV, and would like to use it to play audio/video from my computer, over HDMI. Video works fine, but I can't seem to get audio working. I know it's not a problem with the TV or the cable, because my nintendo switch works fine. I don't think it's a problem with my computer's sound card, because I've played sound over HDMI in the past (with a monitor, not a TV). When I do aplay -l the HDMI output is not even detected; I get

**** List of PLAYBACK Hardware Devices ****
card 0: PCH [HDA Intel PCH], device 0: ALC257 Analog [ALC257 Analog] Subdevices: 0/1 Subdevice #0: subdevice #0

Any ideas? what commands should I run to gather more information?

EDIT: here is the output of sudo lshw -c video:

 *-display description: VGA compatible controller product: UHD Graphics 620 vendor: Intel Corporation physical id: 2 bus info: pci@0000:00:02.0 version: 07 width: 64 bits clock: 33MHz capabilities: pciexpress msi pm vga_controller bus_master cap_list rom configuration: driver=i915 latency=0 resources: irq:160 memory:e7000000-e7ffffff memory:c0000000-cfffffff ioport:e000(size=64) memory:c0000-dffff

Know someone who can answer? Share a link to this question via email, Twitter, or Facebook.