That's a really good site too, though I suggest using fedipact.veganism.social if you're specifically interested in which instances are defederated from Threads. Some instances have hidden blocklists and won't show if they have defederated Threads if you search through defed.xyz.

For example: You can only see that retro.pizza and masto.ai have hidden blocklists if you look through defed.xyz. However, if you look on fedipact.veganism.social, you can see that retro.pizza has joined the Fedipact against Threads, while masto.ai is fully federated with them.