Does the advance pdf support flex? I try to create 1 page with 2 columns but didn't succeed

I don't know what flex is in this context but you can certainly create column data using tables and css.

BFO only supports CSS 2.0 (and even then just a subset of it). See: https://bfo.com/products/report/docs/tags/

Make a table w/ 1 row and and 2 td elements and within those td elements create a new table and you can use the CSS to do your thing.

I want to create it like this, so the content in column 1 will continue to column 2