comments:
HDMI 2.1 support over USB-C/ Thunderbolt is very very new to macOS, as in just starting with macOS Tahoe. My understanding is that this requires M2 or newer, so I don't believe your M1 Pro MacBook will be able to support this functionality properly. It should work on the M5, however. Also, is your Tahoe installation up-to-date? This functionality was broken with 26.1 and 26.2 I believe. The other angle here is that macOS' HDMI 2.1 implementation is unique and requires cables and adapters to support unique features to accomplish this, so most USB-C to HDMI 2.1 cables/ adapters do not work. Your cable may be different, but this UGREEN listing I found says it will not support more than 4k60hz on macOS. I do not have a list of cables/ adapters that work, but I do know that our HDMI 2.1 adapters can work (we sell both an Active DP 2.0 to HDMI 2.1 adapter and a USB-C to HDMI 2.1 adapter). We made a revision to our adapters to support this functionality, so there are some old units out there that don't work, but purchases from our US Web Shop are guaranteed to come with the update, and I've heard success from multiple customers ordering from Amazon (though I'm almost positive they're still holding at least some old stock, so your mileage may vary). Anyways, I hope this helps. Let me know if there's anything else I can assist with.