What I want is this: make a feed from site A,B,C and filter articles with #X in the title and let that (title, date, summary, link) stream into Google Sheets to make a Glide app. Any ideas?
Is this feed dynamic?
Yes, it would be a combination of RSS-feeds.
This will do the trick:
You can use RSSground to create feeds, automate feeds and combine feeds. I use it every day. You can also customize feeds to meet your needs. Hope this helps!