Issues with the review feature

In your screenshot the twistie (arrow head - greater than symbol) is below the + sign.

The whole process is described in The RoboHelp Tour on my site. Look in 2020 section.

It seems like there is no topic in your shared review file.

I just tried this new feature by myself and it worked fine (Trial version on macOS - love it! Purchasing for sure!!):

1. Set up a new review package (in the RoboHelp UI, click the Review tab, then click the "+" in the "Active Reviews" panel) and name it
   [by the looks of it you surely did that step and named that package "Révision"]
2. That package opens a list of all your topics in that project;
   pick at minimum one of the topics by ticking the checkbox (will be blue with a white tick mark after ticking)
3. Click the "Share" button
   --> RoboHelp packs the package 
   [Did that works out fine on your test? It takes a while, even if there's just the Default topic with 2 lines of text in it!]
4. When RoboHelp is ready packing your topics into the Review package a pop-up dialog lets you share a link with others by mail, and you can choose whether it's only working with those specific mail address (private review) or that would be a link that can be sent to third parties and would still be working (public review).
   [Which kind did you use for your test?]
   --> The receiver(s) can open that interface you're showing in that screenshot out of an "Open" button in a mail 
5. If there's an minimum one topic in that package, there should be an arrow heading left (looking like a "greater than" character) at the end of the line where the package name (in your case "Révision") appears. 
6. Click on that arrow
   --> The package opens and the list of topics included there will show up
7. Double-click on (one of) the topic titles in the left panel to open it
   --> The topic content shows up in the center, and on the right there comes up a panel with the commenting tools (and the list of comments already written, if any)