If you are sure you have an SFC2021 account, make sure you are logging in with the correct email/userid and the correct URL: https://webgate.ec.europa.eu/sfc2021/sfc-fo/home.
If you do not have an account, follow the instructions in the FAQ: SFC2021 - I'm new to SFC2021, what do I need to do? | SFC Support Portal (europa.eu).
If you require further assistance contact the SFC SUPPORT TEAM via the contact form on the portal.