Basically on my Huawei Mate 20 I am using Gmail. When I get an e-mail with an attachment and download it, it always goes to the "Downloads" folder. But I want to be able to choose the location each time I download an attachment. Is it possible?
No, the Gmail app doesn't have this feature of choosing download location.
Instead of using the Gmail app, open the website on google chrome. In Google Chrome's settings, go to Advanced Settings section and click on Downloads. There, you can choose to ask the download location for each file or change the download location for all files.