Hello,
If you tick the ‘Enable stock management at product level’ box on the ‘Inventory’ tab for a product and choose the ‘Allow, but notify customer’ backorders option, then the stock column of the product table will display an ‘Available on backorder’ notice. The customer can then purchase the product in the usual way.
https://ibb.co/GsYxzJq
If you do not tick the ‘Enable stock management at product level’ box and simply set the Stock status to ‘On backorder’, then the stock column of the product table will label the product as being ‘In Stock’, with no indication that it is only available on backorder.
https://ibb.co/x5cSSvV
Best Regards.