The core columns block doesn’t use multiple innerblocks. The core columns block is just nested blocks so core/columns is a block and core/column is another block nested within it then blocks get further nested within the column block.
Buttons work the same way core/buttons is a block and core/button is a block nested within it.
For columns, you’d probably be better off trying to utilize the core/columns block and set it up with a innerblocks template that uses it vs. creating your own columns in ACF but there may be a reason you’re avoiding use of the core block. It’s just “backing up” your idea of where InnerBlocks would start and enveloping the container in it and working off the nested block concept vs. framing it as any block-based area would be its own innerblocks area. Not sure if this helps or just makes things worse haha
