I had the same issue when moving from an iPhone 12 Pro Max to the iPhone 13 Pro Max. On top of the continually running out of storage space because “Other System Data” would go up to 60GB apps seemed to get kicked out of ram a lot more often than on the 12 Pro Max. I finally found out what was causing it. I went into the music app and went into the Library tab. Then click on the Downloaded menu option. In there was another menu option that was called Downloading or something and it had the busy sign on it and some films and tv programs were showing for some reason. I cancelled / deleted them all and since then no more issues. Storage is back under control and apps aren’t being kicked out of ram. Maybe this is the reason some other users are having this issue.