Currently, Steam doesn't offer a setting to automatically place new downloads at the end of the queue. By default, when you start a new download, it interrupts the current one. Many users have expressed interest in a feature that would allow new downloads to be added to the end of the queue instead of pausing ongoing ones. While this feature isn't available yet, it's a common request among the community. Steam Community. As a workaround, you can manually pause the new download and resume the one you want to prioritize. Alternatively, you can adjust your download settings to manage bandwidth usage and scheduling. Navigate to Steam > Settings > Downloads and explore options like setting bandwidth limits or specifying auto-update times.
steam support. For more information and community discussions on this topic, you can visit the Steam Community thread.

I see, too bad I guess. Thank you for the clear answer.

引用自 balanco：

I see, too bad I guess. Thank you for the clear answer.