Mongodb will not run on MacOS

I have been happily running MongoDB for years on my mac (currently sonoma 14.6.1), installing via brew, using

$ brew install mongodb-community

(and variants) in the terminal and then starting it using

$ brew services start mongodb/brew/mongodb-community

and getting a nice message:

Successfully started mongodb-community (label: homebrew.mxcl.mongodb-community)

Worked for years, through various upgrades. However, I am running MongoDB as part of a Node application which I have been updating, and this forced me to upgrade my MongoDB setup. And somehow, now, despite the warm "successfully started" message it has NOT started MongoDB. MongoBD should be running on port 27017. It is not:

$ lsof -i tcp:27017

returns nothing. Attempting to connect to MongoDB through Robo 3T, or running mongosh in the terminal, gives some form of this message:

MongoNetworkError: connect ECONNREFUSED 127.0.0.1:27017

(from mongosh, in the terminal). Investigating further:

$ brew services list

returns this:

Name Status User File

mongodb-community error 4 peter ~/Library/LaunchAgents/homebrew.mxcl.mongodb-community.plist

So I go to look at the plist:

<?xml version="1.0" encoding="UTF-8"?>
<!DOCTYPE plist PUBLIC "-//Apple//DTD PLIST 1.0//EN" "http://www.apple.com/DTDs/PropertyList-1.0.dtd">
<plist version="1.0">
<dict>
    <key>Label</key>
    <string>homebrew.mxcl.mongodb-community</string>
    <key>ProgramArguments</key>
    <array>
    <string>/usr/local/opt/mongodb-community/bin/mongod</string>
    <string>--config</string>
    <string>/usr/local/etc/mongod.conf</string>
    </array>
    <key>RunAtLoad</key>
    <true/>
    <key>KeepAlive</key>
    <false/>
    <key>WorkingDirectory</key>
    <string>/usr/local</string>
    <key>StandardErrorPath</key>
    <string>/usr/local/var/log/mongodb/output.log</string>
    <key>StandardOutPath</key>
    <string>/usr/local/var/log/mongodb/output.log</string>
    <key>HardResourceLimits</key>
    <dict>
    <key>NumberOfFiles</key>
    <integer>64000</integer>
    </dict>
    <key>SoftResourceLimits</key>
    <dict>
    <key>NumberOfFiles</key>
    <integer>64000</integer>
    </dict>
</dict>
</plist>

It appears the problem is the line

/usr/local/opt/mongodb-community/bin/mongod

Yes, there is a mongod in that directory. Trying to run it from the terminal gives this:

$ mongod

Illegal instruction: 4

I see that in MongoDB documentation at https://www.mongodb.com/docs/manual/tutorial/install-mongodb-on-os-x/ there is a note: "macOS Prevents mongod From Opening". I am guessing that is what is happening here. Unfortunately the documentation’s advice on fixing this is outdated, and other attempts to remedy this through changing permissions also fail. Any suggestions most welcome.

Update: August 26, after repeated cycles of install, uninstall of various versions of brew install mongodb-community, I have progressed to the point that running brew services start mongodb/brew/mongodb-community now does NOT say "successfully started". Instead I get this

error:Bootstrap failed: 5: Input/output error
Try re-running the command as root for richer errors.
Error: Failure while executing; /bin/launchctl bootstrap gui/503 /Users/pmr906_1/Library/LaunchAgents/homebrew.mxcl.mongodb-community.plist exited with 5.

Now moving the question over the DBA Stack Exchange.

Update: after doing a complete removal of mongoDB and reinstalling outside homebrew, and then running

mongod –config /usr/local/etc/mongod.conf

I finally got this output in the log file:

"This version of MongoDB is too recent to start up on the existing data files. Try MongoDB 4.2 or earlier."

At last! So I have to go back and upgrade my ancient database through multiple MongoDB releases. Oh well. I don’t understand why none of the logs from the homebrew installations did not give this feedback, but anyway..