Before you update Joomla, please refer to the "Compatible up to:" info on the homepage of www.SEBLOD.com.
→ If the version number matches the new Joomla version, feel free to update now.
This is what our Joomla says in the backend.
There is a moderate priority security issue in Joomla 3.9.19 (and other low priority issues). Patched version is out since two weeks ago. It will be good to know if we can safely update or we must wait until a Seblod update is out.
I've been using Seblod 3.19.0 with Joomla 3.9.20. E.g. see here and here (remove links if not appropriate - simply wanted folks to see these versions in action).