Is there any program that can send iMessages or even just regular SMS messages from Silverblue? I think the answer is probably “no” but the ability to do so from the macOS desktop is something I find really useful, would love to have something similar on Silverblue.
that would be Apple Inc. (iMessage) or cellular service (SMS) to provide such application… that means, unfortunately, the answer is No.
For Android there is Messages for web that can be used to send SMS.
There is KDE Connect which will let you send SMS from an Android phone. Don’t know if the messaging works with iOS though.
Otherewise, there are voip providers who let you send SMS via various interfaces.
And gsconnect for Gnome but not for an iphone