Hi Sue, yes, the abacus range is extremely sturdy and the desk will easily be strong enough. There a couple of reviews on the product page which mention using a sewing machine, as follows:
'Needed a work surface for my sewing machine ideally to blend with other oak study furniture and this fitted into space nicely. Appears good quality. Exceptionally well packaged. Easy to assemble. Simple and practical!'
'I bought this desk for my sewing machine along with the three drawer chest and it is a perfect size. It's the best packed flat pack item I've ever had! Each piece was wrapped in tissue and pieces of hardboard were all around the edges of the main packing box, very easy to put together.'
The Abacus range is incredibly popular and regularly sells out with lots of positive reviews.
Hope this helps.