How I can split text in the_content() into 2 columns?

Did you try css?

<div class="columncontent">
   <?php the_content(); ?>
</div>

Then the css:

.columncontent {
    column-count: 2;
}

Depending on your theme, you could just find a div already surrounding your content too.

There is all sorts of magic there!

https://www.w3schools.com/css/css3_multiple_columns.asp

The only thing I would suggest is that you use media queries, as the 2 columns may be a bit much on mobile. You’ll have to decide that and at what breakpoint you want to use.

tech