Sometimes, a screensaver may not be available to all your Roku devices. (ie. some are explicitly for RokuTV and not for Roku devices.)
This is not the instance for Aquatic Life. I have it installed on all my Roku devices and RokuTV. It shows as available to install (ie. Get Screensaver) on all devices, except for my Ultra 4660. It is currently running on the Ultra 4660, but is not showing in the Streaming Channels Search like all the other devices it is installed on.
So, it has either been/is in the process of being removed as mentioned by @RokuLianna , or has been mistakenly removed/omitted from the Search results as compatible with Ultra devices for install.
Roku Community Streaming Expert
Just another Roku user... I am not a Roku employee.
Insignia RokuTV, Ultra 4660, Premiere+ 3921, Express 4k+ 3941, Streambar 9102