I cannot connect to discuss.online as a home site from Sync at the moment, though I can browse it from other home sites. It is not an issue unique to me. The admins of the instance have come to the conclusion it is a lemmy/3p client issue rather than an instance issue, and that clients it breaks now will break more completely with future lemmy rollouts.
Seconding this. I switched over to discuss.online recently and was surprised when I suddenly couldn't use Sync. Took a good while before I happened upon the admin post about the issue so now I'm back to Lemmy.world on Sync