Unfortunately, at least as far as I can work out, Ubuntu does not provide an RSS feed for PPA package pages. Thankfully, FreshRSS does include a web scraping method, using HTML + XPath.
These are the settings I'm using for the UbuntuGIS packages, which I use on this website for gdal:
Feed URL: https://launchpad.net/~ubuntugis/+archive/ubuntu/ubuntugis-unstable?field.series_filter=noble
Type of feed source: HTML + XPath (Web scraping)
XPath for finding news items: .//table[@id="packages_list"]/tbody/tr
XPath for item title: descendant::td[1]
XPath for item content: descendant::td[2]
XPath for item author: descendant::td[3]/a
XPath for item date: descendant::td[3]/time[@datetime]