The Cylc 7 compatibility mode (which allowed workflows to run under both Cylc 7 and 8) has now been removed in Cylc 8.7.0.
See Cylc 7 Compatibility Mode for more details.
As part of this change, the version of Jinja2 that Cylc uses has increased From 3.0 to 3.1+. As a result, any use of deprecated Jinja2 interfaces may break with this Cylc release.
Additionally, support has been removed for reading Cylc 7 workflow databases in the cylc workflow-state command and workflow_state xtrigger.
Deprecated Cylc 7 configuration syntax remains supported, though deprecation messages have been updated to announce the intended removal of support in Cylc 8.9.