It’s on the ‘Edit Category’ admin page, e.g. [host]/wp-admin/term.php?taxonomy=category&tag_ID=1&post_type=post. Theme is not relevant; it’s reproducible with the Twenty Twenty theme. I’ve double-checked with all other plugins disabled.
The issue doesn’t affect the visual appearance of the category editor page for posts, but does affect the apparance of the product category editor page for WooCommerce product categories, because, as a result, additional fields added by WooCommerce are not in the table.
However, the invalid markup can be seen in both cases via ‘Web Developer > Page Source’ in Firefox (see https://www.qzdesign.co.uk/filetransfer/category-editor-markup.png – the errors are highlighted in red by Firefox itself). The extra <table> start tag is not permitted here because it is not within a table cell (td or th) – it doesn’t nest the tables but causes the first one to be closed and a new one to be started. The additional </table> closing tag means the fields added by WooCommerce are not in a table at all.