The first row of tables is always rendered as <thead>...<th>

[fraserbennett]

...even if the Notion table "Header row" control is set to "off". First row text is bolded and centered. Example:

https://www.notion.so/hattonjohn/Creating-a-New-Book-ed42d324123249e5b20fcbf66160f40d

https://docs.bloomlibrary.org/creating-a-new-book