ODK Collect can be launched from external applications as described in the documentation. This documentation uses actions and data which is the supported approach. We have seen some integration applications that use activity names directly. This will be explicitly unsupported starting in Collect v2021.3 (mid-fall 2021). In particular, the FormEntryActivity will no longer be exported.
In Collect v2021.2, launching FormEntryActivity directly will not work with multiple projects (Collect will be left in an unpredictable, bad state) though it will continue to work as before if there is only one project configured in Collect.