Normal behavior using the block editor is to not add any attributes at all, which is an implicit dofollow. You don’t really need dofollow as long as there is not anything contradictory like a robots nofollow meta tag.
If your links have a nofollow attribute, it was added by either your theme or a plugin. It could even be Elementor itself, IDK. You need to identify what and how the attribute is added in order for it to be removed or changed to dofollow.
To narrow down the source, switch to the twenty twentyone theme and deactivate all plugins. You’ll now see that adding a new external link via the block editor includes no attributes. Restore your theme and plugins, one at a time, until adding links results in nofollow attributes again. Take up your question through the dedicated support channel of the last activated module, the one responsible for adding nofollow.
