Disclaimer: Make sure you backup your db's in case you need them later because running these commands will delete all your local Postgres databases.
First you need to run:
$ brew uninstall postgres
$ rm -rf /usr/local/var/postgres
$ rm /usr/local/var/log/postgres.log
$ rm -f ~/.psqlrc ~/.psql_history
If you want to make sure there are no other Postgres-adjacent Homebrew formulae still installed you can eihter check via:
$ brew list --formula | grep -e postgres -e psql
or search your entire system for file name matches:
$ sudo find / -name "*postgres*" -o -name "*psql*"
Before reinstalling postgreSQL it might be a good time to reboot your machine. After the reboot run the following commands to get your fresh installation of postgreSQL:
Make sure your Homebrew is fully updated and give Homebrew a chance to diagnose any problems:
$ brew update
$ brew doctor
The diagnostic command $ brew doctor
should exit cleanly with the simple message 'Your system is ready to brew.'
Now you can reinstall postgreSQL and see if it runs via:
$ brew install postgres
$ brew services start postgresql
Source: https://blog.testdouble.com/posts/2021-01-28-how-to-completely-uninstall-homebrew-postgres/