It is now possible to connect to ECC with 1.20.4 on your Minecraft client.

However, we still recommend that you use 1.20.2 when connecting to our Main & other servers, and 1.12.2 when connecting to Skyblock. This compatibility update is primarily for new players who are looking for servers on their 1.20.4 clients.

You are free to report any bugs that come with running 1.20.4 at https://ecc.eco/help.
However, the issues will most likely already be known/reported and we, again, advise you to use 1.20.2 if you want to avoid such issues.

This is not a server update to 1.20.4! This thread/update only pertains to your ability to connect to ECC with a 1.20.4 client. New features (blocks, mechanics, etc.) that may or may not come with 1.20.4 are not yet implemented by this update.