Update brew, install mongodb community version, create a new directory outside root since >=catalina apple wont let you put data in the root directory then update your mongo conf.
sudo mkdir -p /System/Volumes/Data/data/db
sudo chown -R `id -un` /System/Volumes/Data/data/db
brew uninstall mongodb
brew tap mongodb/brew
brew install mongodb-community
nano /usr/local/etc/mongod.conf
When the nano opens change the path change dbPath /System/Volumes/Data/data/db
Add some alias's if you want to get fancy.
alias mongod='brew services run mongodb-community'
alias mongod-start='brew services start mongodb-community' #will start MongoDB automatically when you login into your Macbook
alias mongod-status='brew services list'
alias mongod-stop='brew services stop mongodb-community'
Restart your terminal and then voilà you're in there like swim ware.
If you added the alias you can start mongo and check your dbs.
mongod-start
mongo
show dbs