Good afternoon.
The site now has the ability to download the cattr client v3.0.0-RC4 https://cattr.app/desktop/
But it turned out that this version of the client does not know how to work with the server part of cattr v3.4.3.
And if you enter the documentation https://community.cattr.app/public/t/general in the "Getting started" section, then they advise you to download a script that refers to the outdated amazingcat/cattr v3.4.3 (Updated 2 years ago) https://hub.docker .com/r/amazingcat/cattr/tags . Which does not work with cattr desktop v3.0.0-RC4