Cool, I’m glad you found something that works for you. So you know, I have a 2018 12.9” Pro, and the bookmark sidebar does indeed stay open after selecting a link. An example of where it may be beneficial: searching through your history to find a specific page you visited within a series of pages for the same domain. Another example: split-view style reading list where your articles are in the left column and your article content is on the right. I can’t remember a time the bar hasn’t stayed open, but I also don’t use it often. I opt for favorite links from the new tab display the majority of the time.
You're talking about Safari, right?