You first need to identify why you need an advanced search. Keyword searching, whether in basic search boxes or advanced searches depends on relating keywords using AND (search engine must include all your search words in every result), OR (either word can appear in search results, even if not both), NOT (don't provide any results with this word in them) and phrase (usually done by putting quotation marks around the phrase). In most cases, you don't need an advanced search. PubMed has an advanced search that lets you set up your ANDs and ORs, etc.
If you are looking for a better search tool than PubMed, you could try Dimensions (https://app.dimensions.ai/discover/publication) which has only a basic search but allows you to limit with various filters, including one for open access results only. It is a very large database of scholarly articles and other resources, and it's free to use.