I’m not aware of any means to actively prevent the adjust of column widths, either within or outside the contents of the Tabbed Page widget. In the few models I tested here, in developer and end-user mode, I was able to drag column width to any preferred width. Whether it got stored between sessions, depends on the UI being editable or not.

You also seem to suggest it does not always happen to your Tables within Tabs. Do you have any idea what the circumstances might be, or a simplified model you could share and which exhibits this behavior?