You should be able to perform a search using the Advanced Search page by using a browser in desktop mode. Most mobile browsers have an option you can reach through a three-dot menu that allows a browser tab to render pages in desktop mode.
Many advanced search features are also available by other means if you do not want to perform a search using the Advanced Search page. You may also be able to save a search made using the Advanced Search page, and then open the same search using a mobile browser in other modes or using the eBay app.
