Unfortunately eBay rarely removes listings that are in the wrong category, even when such things are explicitly reported.
Your best bet is likely to find a way to specifically narrow your search to items you are interested in and to avoid items you are not.
One way to avoid many miscategorized items in a particular category is to search the category by keyword -- possibly using the category name as the search keywords if you want the broadest possible coverage of the category -- then selecting several appropriate filter options (not including the "not specified" option). Selecting item conditions and avoiding "new" item condition may also help when searching for antiques other than New Old Stock.
The more filter options you select, the fewer miscategorized items are likely to appear in your search.
For instance, here is a search of antique furniture:
https://www.ebay.co.uk/sch/i.html?_nkw=antique+furniture+&_sacat=20091&Antique=Yes&rt=nc&_odkw=antiq...