Hi @Ankur
Per my research, there is no such api can reach your requirement in graph. As a workaround, I would recommend you to use rest api to list all sites which is either a hub site or associated with a hub site. Please refer to following url
Query: contentclass=sts_site
Refinement filter: departmentid:string("{*",linguistics=off)
Trim duplicates: false
REST: /_api/search/query?querytext='contentclass%3dsts_site'&refinementfilters='departmentid:string("{*"%2clinguistics%3doff)'&trimduplicates=false
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