Really enjoying this building with blocks series of posts. Even though I’ve done some deep dives of my own it’s still really interesting trying out the things you write about here.

For your original abandoned pattern I tried it with the 50/50 columns block, but gave the first column a width of 500px and the width of the second column was left empty, and made sure to toggle off the ‘Stack on mobile’ option.
The result wasn’t too bad, with the left-aligned content maxing out at 500px and the width of the second empty column going progressively down to zero on smaller screens.