Moving to Gutenberg…

Hi. I have a couple older sites that are using the classic editor plugin. They are running the latest WP and from what I understand the themes are Gutenberg compatible. I am thinking of moving them to Gutenberg.

If I just flip the switch, disable classic editor and start using Gutenberg moving forward, is there anything I need to know in regards to my older posts?

As I understand it, older posts won’t be converted to blocks unless I go into them and re-update them. So, they should stay the same. Is this a correct way to think about it?

Thanks.