First, I think sorting PRs by "recently updated" can be a good proxy for "does anyone care about this PR"... If it's being bumped and reviewed, it is.

But also definitely start setting up linting rules / labels to indicate how healthy or close something is to being merged.

The goal is to limit work-in-progress, and focus on getting PRs that are easy to merge over the finish line.

Edit: and yeah, a weekly review cadence goes a long way to triage tickets and PRs and get some initial feedback to developers. I also like the "next review on this date" proposal to push certain problematic PRs to a slower cadence so they're not occupying too much bandwidth.