I've been banging on a drum for the past decade that the industry needs to switch to asynchronous review.

You allow self review and optional external review of code but the default is that the engineer can ship to production without a review block.

Then you either do post merge review: have a review column in jira or whatever where people are assigned to review and can complete on their own schedule in a non disruptive and non blocking way. This also avoids piling reviews onto whoever has the best rubber stamp.

Or

You switch to a quarterly system review meeting where you as a group go over and suggest improvements to make in the codebase holistically.

I've seen both of these work extremely well and with AI you can basically automate the review process to the point it's pretty much pointless having a human review step.

The only other way to avoid the issue of people sitting on thumbs waiting for review is to have everyone prioritize reviewing code ahead of producing new code. This works but is incredibly disruptive to the reviewer and has side effects like review bombing on the largest rubber stamp reviewer.