I see people are doing scripts or other things to remove shorts from their feeds, but there is a simpler solution.

Take your RSS URL of a channel, e.g.:

https://www.youtube.com/feeds/videos.xml?channel_id=UCxSGC9B...

Replace the `channel_id` with `playlist_id` and replace `UC` with `UULF`. This prefix will only list normal videos:

https://www.youtube.com/feeds/videos.xml?playlist_id=UULFxSG...