How can I allow only certain roles to join temporary channels?
There are different solutions to this:
Without changing any bot option: simply open the Master Channel's settings on Discord. In the Permissions tab, add the role you want and give it the Connect permission.
Secondly, edit the @everyone role and make sure Connect is denied.
Change permission syncing to category
In the dashboard, select your server -> select your Master Channel. Here, find Permissions Syncing and set it to Sync permissions from the category.
On Discord, you can now edit the category where the channels are created: in the permissions tab, add the role you want and give it the Connect permission. Secondly, edit the @everyone role and make sure Connect is denied.
With this method, you can configure the bot so that only some roles can join the temporary channels, but you can also choose different roles that can create the temporary channel by editing the Master Channel's permissions on Discord.