Borrowed components - instances: Input for the filter, Button for Columns and the pager, Checkbox on every row
Using the Data Table
Why does it have no variants at all?
Because what varies in a table is its data and its columns, and neither fits in a variant dropdown. Drawing Rows: 5 · 10 · 20 as an axis would triple the file for no gain, since you edit the rows either way. It is the one component here published as a finished thing.
Are the rows instances of the Table component?
No, the rows and cells are local boards. Table is published separately with its own cell variants, but a data table needs column widths you can drag, and a local board lets you do that without detaching. What is borrowed is everything interactive: the filter is an Input, the Columns and pager buttons are Buttons, and every checkbox is a Checkbox.
Why is each row 41 tall and the head row 40?
The extra pixel is the rule. Every body row carries its own 1px base.border along the bottom rather than the table drawing dividers between them, so deleting a row takes its rule with it and nothing has to be tidied up afterwards.
What sits in the last column?
A 44px cell holding Tabler's horizontal dots, the row action menu. It is centred on body rows and empty in the head, which is why that one cell is the only place where the head row and the body rows do not line up their alignment.