I'd like to know if there is a way to query all the assets of which the account is the issuer.
Yes, it's possible. You can use
/assets endpoint. Do not forget to provide a large enough
limit parameter, as Horizon always return max 10 records by default.
For example, here is the list of assets issued by InterstellarExchange: https://horizon.stellar.org/assets?issuer=GCNSGHUCG5VMGLT5RIYYZSO7VQULQKAJ62QA33DBC5PPBSO57LFWVV6P&limit=100