As a workaround, if you click the ^ button on the top of the Tag Window you can make it take up the entire left pane.
Action Window - Dump Tags display bug (?) in MC ver. 27.0.20:
Click on "Tag" in the Action Window, then click its "Maximize" icon in upper right corner of the Tag Action window to make entire left pane available (equivalently: select a file and hit <alt><enter> or RMB menu Tag).
Now clicking the ^button for Dump Tags only expands the Dump Tags display to about 30% of the available vertical space in the maximized Tag pane (only 10 lines of Dump Tags are displayed at once), necessitating painful over-usage of its scroll bar to examine all entries in Tag Dump if it contains more than 10 lines. Whereas all other tabs in the Tag Action Window make full use of the available vertical space. Dump Tags should behave like Advanced.