Here is a fancy Chrome OS flag for you to test. I am on Canary channel, so it might take a while before it shows up for you. However, when it does show up, remember who told you first!
I enabled chrome://flags/#force-enable-stylus-tools on my Chromebook and restarted it. And voila!
Here is the official description of the flag: Forces display of the stylus tools menu in the shelf and the stylus section in settings, even if there is no attached stylus device.
It might take a while before I can get my hands on a Samsung Chromebook Pro or Plus, let alone use one. For now, I will have to satisfy myself with this menu.
Only two of those options work for me without stylus. I can take screenshots, but not screenshot of a specific region. I can open the newly taken screenshot in Google Keep to annotate. I can also use the “New note” option in the menu to quickly launch the Google Keep app to start writing.
If you have a Chromebook with stylus, do give this a try and let me know if it works!