With the WordPress REST API plugin, use the following curl command line to get and update title and content.
GET a page
curl --user "$WPAPPUSER:$WPAPPPASS" -X GET https://website/index.php/wp-json/wp/v2/pages/<page_id> | jq ".content.rendered"
Update a title
curl --user "$WPAPPUSER:$WPAPPPASS" -X POST https://website/index.php/wp-json/wp/v2/pages/<page_id> -d 'title=My title'
Update the content
content="<!-- wp:paragraph --><p>Hello World</p><!-- /wp:paragraph -->"
curl --user "$WPAPPUSER:$WPAPPPASS" -X POST https://website/index.php/wp-json/wp/v2/pages/<page_id> -d "content=$content"