@Tom_B is telling a true argument.
You want to use Collabora Office in schools ?
You pay for it, you won’t have limitation and you will have support for installing and debugging.
Or you follow some scripts to compile it by yourself with the hardcoded limitation to a higher number.
You can find on this forum a script made by @husisusi i don’t know if it work now for Ubuntu 18.04 for exemple. But i tested it some months ago and it worked : HowTo: Install Onlineoffice on Ubuntu/Debian (No Docker No Limitation) (if you want to run it on 18.04 https://github.com/husisusi/officeonlin-install.sh/issues/159)
You also have the docker version of LOOL (LibreOffice On Line) who was updated 20 days ago, the docker version of CODE was updated more than 2 months ago…
LibreOffice 6.1 brings a lot of improuvements but i am still waiting an update of LOOL or CODE for seeing if i will leave OnlyOffice or not.