Shelter may have been taken down a while ago, not sure if by Google or the developer.
According to the Island developer Island was removed because it’s not supposed to use
REQUEST_INSTALL_PACKAGES, so it’s probably the same for Shelter. They’re appealing but if/when it returns it might be “with limited functionality” which one would be able to restore with an “extension” downloaded on github but at that point why not just install the apk from github in the first place.
As for Shelter and Insular (fork of Island), they’re also available on F-Droid.
Wonder if they’re cracking down on these “hacks” to leverage the work profile on purpose, like they do local VPNs that block ads.
Ugh.
Thankfully Island is available on Github, and Shelter and Insular are on F-Droid.
I rely on Island for having two copies of apps like WhatsApp since Google can’t be bothered to offer this feature on Pixels like Samsung, OnePlus, etc. do.