TMC Self-Managed is integrated to OIDC-compliant user identity provider. However, when user click on logout, the user session is not terminated. If the user click on login on TMC UI again, user will be redirected back to TMC main page without additional login required.
It's a limitation of OIDC itself. Logging out of one client app (e.g. TMC-SM's UI) does not log you out of your session with the OIDC provider itself.
It's expected behavior for the OIDC integration. You can logout completely from the OIDC provider UI.