Why is the imca.tv channel no longer available?
This is a question for imca.tv. Per this page, the only streaming device platforms they currently support are Firestick and Chromecast.
Edited to add:
Was this an uncertified "private" channel that was installed by entering a custom code on your account page at my.roku.com?
Effective Feb 23, 2022 Roku discontinued support for ALL uncertified (often called "private") channels. This has nothing to do with the content of the discontinued channels (despite what some of their developers may tell you). It is a removal of ALL channels not certified by Roku. The entire non-certified channel system has been replaced by a new system using a new Independent Development Kit (IDK).
This was not done without warning. Developers had advanced notice giving them 4 months to submit new versions of their uncertified channels that met Roku's requirements for certification.
From the Roku announcement for developers from October 2021: "Sunsetting non-certified channels With the release of the IDK and beta channels, Roku will remove non-certified channels from the platform by March 2022. The Roku IDK and beta channel feature will facilitate broader innovation, improve beta testing, and offer a better development experience and a more standardized development process across streaming platforms." Full announcement: https://blog.roku.com/developer/idk