That would be possible but you’ll need custom code.
One approach is to create a custom field with the help of ACF: https://www.advancedcustomfields.com/resources/getting-started-with-acf/
You’ll need to add a “subtitle” field for your posts. Then, manually move the “second part” of your title to that field.
Then, go to Appearance > Elements > Global Posts Headers, and add a GB Headline Block. Enable its Dynamic Data and set the source to post meta – and set your custom field.
This should assure that there’s a definite first and second part for your titles.