Go to your admin panel and click on Nodes
Then click Create Node
Type = Search forum
You will have the option then to exclude specific forms:
Once you have created that forum you can go to it in the forum list and you will see just the threads from all other forums you didn't exclude.
You can use the URL of that forum as your RSS feed and the feed will show the latest x threads from that search forum (which excludes the forums you don't want)
You don't need to actually have it in the node list, you can untick that in the Node settings once you have the URL copied via the browsers field .
NB: this works for an RSS feed into my Wordpress site, I can't verify how it is with iftt in Twitter as I don't know what that is. All I know is it seems to work as normal RSS feed.