As Flex is a commercial distribution of the Janssen Project, check the Janssen Nightly Build changelog and issues. You can also check the Nightly Build changelog for the Admin UI. Gluu 4 is considered a stable release–meaning no major features are planned.
Gluu Flex – Q3 2023
Gluu 4 – Q3 2023
Gluu Flex – Q4 2023
Gluu 4 – Q4 2023