Hi, Big differences, please read blog posts related >> https://www.joomshaper.com/blog/sp-page-builder

The major change is only ONE front-end editor view compare to SPPB 3.8 where you had back-end and front-end editor. But If you have production site, not testing ,I recommed waiting to SPPB 4.0.6 version at least.

SPPB 3.8 code will be supported/updated till Sep 2023 like Joomla 3.10 itself, so you have a lot of time to upgrade decisions.