Which save dialog are you referring to? I'm aware of OBS taking it's sweet time to unfreeze the OS e.g. when browsing for a media file for a media source.
As it is, these file browse dialogs are locking up the entire system, with a few seconds of responsiveness sprinkled in before locking the system up again.
Once the dialog is closed, the system is fully responsive again. Until then, you need to have a lot of patience..
