I currently use Nextcloud News, but it's a bit slow (especially with my 50k+ unread items), and doesn't support dynamically ranked feeds, only chronological ones. It's nice having read status synced across devices, though.
No, it doesn't. What you can do is use an RSS proxy to create your own feeds of any site and read that through Nextcloud News. I do this for a few specific sites and purposes - e.g. custom searches on auction sites.
As to Nextcloud News being slow with 50K unread items I wonder whether there's something else amiss as I have close to 600K unread items without undue slowdowns.
The only real slowdown I notice in Nextcloud News is caused by a dog-slow piece of javascript in news/templates/part.content.php which causes a delay any time an item is clicked in the feed. This can be solved by removing everything related to 'sharing' (i.o.w. everything after </time> in the list div (class=utils), make sure to balance those tags...). News is much faster in use that way and since I never use the 'sharing' related stuff - if anything needs to be shared I can just share a link instead - nothing of value is lost.
I currently use Nextcloud News, but it's a bit slow (especially with my 50k+ unread items), and doesn't support dynamically ranked feeds, only chronological ones. It's nice having read status synced across devices, though.