Thank-you, Saguaros.
I will wait until the next full update with this fix (And the hamburger side menu fix).
On the same blog grid page there is also this error at the start of each item block.
<div class="item column-<br />
<b>Warning</b>: Undefined variable $rowcount in <b>C:\Users\info\OneDrive\Documents\HTML\xampp_8_0_12\htdocs\xxxxxx\plugins\system\t4\themes\base\html\com_content\category\blog.php</b> on line <b>123</b><br />
" itemprop="blogPost" itemscope="" itemtype="https://schema.org/BlogPosting">
I think this is newly introduced as I also use a custom version (as an over ride) of this page using the previous version t4 code and this error was not there.
D.