As has been pointed out, :nth-child is not supported in Gmail and Outlook, or Yahoo or Protonmail (except PM iOS).
You could achieve this manually via the adjacent selector combinator (e.g. tr + tr), which adds most Gmails (not Gmail accounts without a Gmail address) as well as Yahoo (see https://www.caniemail.com/features/css-selector-adjacent-sibling/)
<style type="text/css">
tr + tr + tr + tr + tr + tr + tr + tr + tr + tr + tr + tr + tr,
tr + tr + tr + tr + tr + tr + tr + tr + tr + tr + tr,
tr + tr + tr + tr + tr + tr + tr + tr + tr,
tr + tr + tr + tr + tr + tr + tr,
tr + tr + tr + tr + tr,
tr + tr + tr,
tr
{background-color:red}
tr + tr + tr + tr + tr + tr + tr + tr + tr + tr + tr + tr,
tr + tr + tr + tr + tr + tr + tr + tr + tr + tr,
tr + tr + tr + tr + tr + tr + tr + tr,
tr + tr + tr + tr + tr + tr,
tr + tr + tr + tr,
tr + tr
{background-color:transparent}
</style>
Tested with the following table structure:
<table>
<tr><td>And stuff</td></tr>
<tr><td>And stuff</td></tr>
<tr><td>And stuff</td></tr>
<tr><td>And stuff</td></tr>
<tr><td>And stuff</td></tr>
<tr><td>And stuff</td></tr>
<tr><td>And stuff</td></tr>
<tr><td>And stuff</td></tr>
<tr><td>And stuff</td></tr>
<tr><td>And stuff</td></tr>
<tr><td>And stuff</td></tr>
<tr><td>And stuff</td></tr>
<tr><td>And stuff</td></tr>
</table>
