Upgrade - Milestone?

Hey

i currently have Arcos Milestone on my MyCloud2EX Ultra running. it was on it after i bought it.

I run OS 3.
When i upgrade to Version 5 will it stay on the Device?
If not how can i re-install it?

@diederit The Milestone Arcus app is no longer available or supported on My Cloud OS 3 since 2018 and is not supported on My Cloud OS 5.

What alternatives for Video Survialance do i then have for my MyCloud?