Not sure which version you are using but 19 is not up to date in your signature. I seem to remember this was happening sometimes with the original build 3003.
Also check that you have read write delete and rename access to the folder you are saving too
Archicad 4.1 to 26 Apple Silicon you can't build a line Mac Studio iPad Pro iPhone
OS X won't let you install an older version of java so you have to manually delete it.
To do so open and terminal and enter these two commands:
sudo rm -fr /Library/Internet\ Plug-Ins/JavaAppletPlugin.plugin
sudo rm -fr /Library/PreferencesPanes/JavaControlPanel.prefpane
then install the correct java version given by the first link.
you should then be able to save you file as usual.