IE11 is no longer supported for Confluence Cloud. Support was ended on 31 March 2020.
See: Retiring IE11 support for Atlassian cloud, server, and data center products
IE11 will be supported until the last version of Confluence that supports IE11 has reached end of life (EOL) (See: When is this happening?).
The last Confluence version to support IE 11 is 7.4. Support was ended in 7.5 (See: End of Support Announcements for Confluence).
Confluence 7.4 will be EOL 21 April 2022 (See: Atlassian Support End of Life Policy).