How to fix "waiting for other installations to complete"

I was trying to install an app (MS Teams) but was seeing a strange message from the installer:

waiting for other installations to complete

I found something on on how to fix it and it worked like a charm:

sudo killall -1 installd

Note: I did not run the command to remove any locked files, just killed the process and tried the install again.

Hopefully this helps someone else (or future me).