UHD output performance to UltraStudio 4K Mini is unusable on macOS Intel, perfect on M1

Operating System Info

macOS 12

Other OS

No response

OBS Studio Version

Other

OBS Studio Version (Other)

27

OBS Studio Log URL

https://obsproject.com/logs/9PmYBd-le9uIxrSR

OBS Studio Crash Log URL

No response

Expected Behavior

Smooth rendering of key/fill playback on output

Current Behavior

Stuttered output that drops in performance quickly. Set to 29.97 it's playing maybe 20 fps but quickly drops to 1 fps and lower.

Steps to Reproduce

1. macOS 12.4 Intel Mac Pro, OBS 27.2.4
2. install thunderbolt Blackmagic UltraStudio 4K Mini,
3. Set OBS to 3840x2160 29.97 canvas and output, enable RGB in advanced settings
4. enable keyed output for UltraStudio. Play something that has alpha channel, and motion
5. Performance starts slow, and gets worse. Totally unusable.

Anything else we should know?

1. Exact same setup (Intel Mac Pro) but using Decklink 8K card instead of UltraStudio works perfectly fine
2. Exact same setup (UltraStudio 4K Mini) but using M1 MacBook Air instead of Mac Pro works perfectly fine

Start by reviewing the linked OBS log and reproducing the keyed UltraStudio 4K Mini output on macOS 12 with an Intel Mac. Compare the Intel and M1 behavior, and the UltraStudio and DeckLink setups; done means smooth 3840x2160 29.97 playback without rapidly falling frame rate.