Some users have reported issues using Jaikoz on MacOS Big Sur, especially with opening the Preferences window. It seems the issue is caused by a new default setting in Big Sur called Prefer tabs, the default seems to be in full screen. This means the problem occurs when you maximize the Jaikoz main window (with the green light in the top right hand corner of the Jaikoz window) , but Jaikoz should be okay when the window is not maximized.
But If you set it to never that should solve problem, conversely if you set it to always then the problem will always occur. I am looking to see if there is a way I can have Jaikoz ignore this setting for next release so Jaikoz is unaffected by it.
We are waiting for a fix to be be made in the underlying Java https://bugs.openjdk.java.net/browse/JDK-8256465 so that you don’t have to change this setting.