Steps to reproduce the issue

In an admin list view use the table.columns script to enable user to select columns to display and include either <tfoot> or colgroup elements in the table

Expected result

table.columns should work as it does for tables that don't have tfoot or colgroup elements

Actual result

the layout breaks with empty space at the right for the hidden columns and if <colgroup> is in play the classes and styles screwed up

System information (as much as possible)

Joomla 5.1 (and presumably 4)

Additional comments

This is slightly tricky to fix - I made a start but got lost and ran out of time so simply abandoned using table.columns.js in my J5 components - which is a shame since the core components are using it.

A simple unsatisfactory workaround would be to amend the script to simply do nothing if either <tfoot> or <colgroup> are present in the table.

A <colspan> anywhere in the table will also break it, but this perhaps could be more reasonably simply excluded as if you think about it it will be impossible to fix.