When adding PluralKit to a new server, it does not request the "Send Messages in Threads" permission by default. It should request this permission by default so that users do not encounter issues using PluralKit in threads.
Using the pk;permcheck <serverid> command returns "No errors found, all channels proxyable :)" message even when the "Send Messages in Threads" permission is disabled. It should return a permissions check failed style message to let users know that there might be an issue with using PluralKit inside of threads.
The user guide does not list the "Send Messages in Threads" permission in the Adding the bot to your server section (last paragraph). It should be included so that users are aware that this permission's configuration can affect the tool's behavior.
The Roles and permissions article does not mention the "Send Messages in Threads" permission. It should be mentioned so that users are aware that this permission's configuration can affect the tool's behavior.