This is also replicable on article pages where there are not enough headers to generate a TOC, such as https://en.wikipedia.org/wiki/Star_Trek_Star_Fleet_Technical_Manual

When I am logged in, this custom CSS seems to prevent the problem (I needed to insert this because the background color I assigned to the TOC sidebar was overwriting the title):

.vector-toc-pinned #mw-panel-toc {
    contain: none;
}

One more note: I added this custom CSS after a MediaWiki CSS update on 2 Feb 2023 caused my left sidebar background to overwrite the page title on pages with no TOC. That might help track down the code change that caused this problem.

In T329174#8597855, @Jonesey95 wrote:

This is also replicable on article pages where there are not enough headers to generate a TOC, such as https://en.wikipedia.org/wiki/Star_Trek_Star_Fleet_Technical_Manual

If you disable limited width mode (The text has to be hard up against the left edge)