MCC on 1.17?

Yes, you will be able to connect with 1.17 soon. This will be updated probably very soon (if not already) Please note that playing on 1.17 may not be the best quality so playing on 1.8.9 (Or 1.12 for Creative and Survival servers) would be better. Information on how to change your version can be found here: https://mccentral.org/community/threads/how-to-change-your-game-version.18105/. However if you don’t want to keep switching between 1.17 and 1.8 then by all means stay on 1.17.

 

It might also be something to do with the Mojang blacklist; so that might be part of it.

In the meantime, as above, you can choose your version and connect in 1.16 or earlier.

We are actively working on it.

Edit: Apparently the best IP to connect with is 'mccentral.org' - so try that and see if it makes a difference.