Hey,
This "/login/signout endpoint logs you out of the Okta sessions that are responsible for maintaining the Okta dashboard. You can read more about it here: Okta Sign out API - #10 by andrea.
You may need to use the Revoke endpoint (OpenID Connect & OAuth 2.0 API | Okta Developer) and revoke the tokens for App1 or App2 based on where the user logs out and ensure the Okta sessions are Intact to avoid loguts…
And also, the right way to logout of Okta is to use the logout endpoint. Eric has summarized correctly that the fromURI parameter may not work as intended. You can read that comment here