If you’re trying to install the unifi controller on linux and you want to use a version of Mongodb above 4.0.0, like 4.4.0, then do the following as su.
You cannot use apt install unifi. You have to get the download link for the latest controller from https://www.ui.com/download/unifi/unifi-ap
Once you’ve got that link url, move into your home folder and download it from that link, something like this:
wget https://dl.ui.com/unifi/6.0.28/unifi_sysvinit_all.deb
Install it:
dpkg --ignore-depends=mongodb-org-server -i unifi_sysvinit_all.deb
Fix the broken packages:
vim /var/lib/dpkg/status
Find this location:
Package: unifi
Status: install ok installed
Remove the maximum Mondodb limitation so that the Depends looks something like this:
Depends: binutils, coreutils, adduser, libcap2, curl, mongodb-server (>= 2.4.10) | mongodb-10gen (>= 2.4.14) | mongodb-org-server (>= 2.6.0), mongodb-server | mongodb-10gen | mongodb-org-server, java8-runtime-headless, jsvc (>= 1.0.8), logrotate
You should be able to log in and configure or restore your new controller.