You can’t find that documentation because it doesn’t exist. It doesn’t exist because that’s not how it works, and it would require extensive duplication to set up.
So to figure out what you need to put, figure out what it is in Javascript/JSON, then translate it to PHP.
The pattern is:
[
'block name'
[
'parameter': 'value'
.... etc
],
[ .... child blocks ... ]
]
Which brings us to why there is no doc that explicitly mentions these parameters for PHP. Those parameters aren’t defined in PHP, they’re defined by the blocks themselves, and the blocks are built in javascript. So you won’t find a list of parameters for use in PHP block templates, because there isn’t one, and it would not make sense to make one. That’s not how it works.
So, build your blocks in the block editor, look at their parameters, then write them in in PHP.
A good way to example my question, how did this person find the answer on how set the width of this template columns.
By inspecting the blocks in the editor to see what the parameters of the block were, and what their values were.