The feed has no natural ending because your attention has become somebody else’s beginning.

A feed does not end because ending it would not serve the people who built it. Your attention is the product being assembled, so the design is aimed at continuation rather than completion, which is why you can put an hour into one without ever reaching a natural place to stop.

Supply the ending yourself, since the thing will not. A timer, a fixed number of items, a rule about which room you use it in. Any external stopping point works, and having one converts an open-ended drift into something that finishes and lets you go.