I found the following: Why is my Hulu such bad quality?
Streaming in 720p depends on the configuration of the device you are
using. Contractual restrictions and digital rights management policies
prevent Hulu from streaming in 720p unless the device as configured is
This led me to find support for DRM that was preventing HD streaming via High-bandwidth Digital Content Protection (HDCP)
The Intel(R) unified HDCP (High-bandwidth Digital Content Protection)
is a user space implementation to prevent copying of digital audio &
video content across digital display interfaces. It provides Linux
user space implementation to enable the HDCP1.4 and HDCP2.2 protection
for external digital display interfaces (HDMI/DP).
I installed the package
intel-hdcp via apt with:
sudo apt -y install intel-hdcp
This seems to have been enough to make my device "HDCP compliant". Hulu is now streaming at an acceptable quality.
Hopefully all of this helps. It is certainly known that there are occasions when HDCP ends up disrupting the streaming experience for paying Hulu customers and this is not always something the user has any control over.