This is quite hard to explain and even harder to search for, so forgive me if this has been dealt with before, and also for what might become a long post!
I am frequently in a position where there might be, say, four teachers on a course. They might always have different students to each other, or it might be the same students learning different things. Moodle does a great job to allow activities, communication, etc. to take place without annoying everyone else who isn't involved. However, I have often been in a position where I have wanted to add a specific activity relating to a specific group on the course that is not relevant to any other teacher or student.
For example, in the summer I was doing an activity involving Padlet, and a large proportion of my students couldn't work with it. I suspect there was a mixture of issues with OS, browser, VPN, country, IT ability etc. It didn't matter, I needed them to be able to respond to the activity, so I set up an assignment activity in the course. This is fine and dandy, but over a 10-week course, if this happens now and again involving multiple teachers, you end up with an awful mess on the course page. The same thing can happen in the forums. Some of these things may need to stay there for weeks, although some will be able to be removed or at least made invisible quite quickly.
So, is there any way in Moodle to allow each teacher an area that doesn't make the course page bigger, longer, messier where they can add activities etc. as they see fit over the length of the course or is Moodle simply not designed that way. Having different courses for each teacher isn't an option.
FWIW I have just upgraded to Moodle version 3.10 and the latest version of the Boost theme.