Glad it’s not just me.
I also created a thread for this issue if you wanted to chime in or be part of hopfully finding a resolution:
https://community.home-assistant.io/t/google-cast-suddenly-wont-display-black-background/823644/2
I originally thought this may be due to 2025.1.0 update but I did this the day before I saw the issue and someone within this thread above is still on 2024.12 so it kinda rules that out.
I just just looked however a little at my log file and it seems to be spitting out cast errors left right and centre but I don’t know if it’s just me.