Sense (in our out of AWS) should not assume the domain, so I don't believe a default is coming from Sense. You can change your authentication method inside of QSE from Windows to Forms in order to force an empty input box if you wish. This is configured in QMC > Virtual Proxies > Authentication > Windows Authentication Pattern.
This is something you can configure via Virtual proxy. From what you explained, would it be better served by using SSO (single sign on, using SAML authentication) for your Qlik Sense environment. Authentication handled by you Identity provider (IP), ex- Azure AD and passed that user on to Qlik sense creating more seamless user journey and removing too many login screens. There are plenty documentations on how this can be achieved. I have also bloged about this subject (however its bit outdated now and AAD config on Azure portal has now more refined). If you would like to go down that path then please let me know. I will dig up sone materials to guide you in the right directions.
Kabir Please do not forget to the mark the post if you find it useful or provides you the solutions 🙂
Quick link to support document which covers SAML authentication for few different identity providers. Might be useful for you. Theres a Google one out there somewhere in the community if you use google. Hope this helps.