I tried to install php 7.4 on my mac osx without homebrew, because I am not able to update homebrew anymore.
curl -s https://php-osx.liip.ch/install.sh | bash -s 7.4
I get the error
Did or could not download package: 7.4-frontenddev
Eyeballing the source for that install script, it looks like when you pass in 7.4, you're telling the script to get PHP 7.4. Unfortunately, it looks like the project has been deprecated as of November 30th, so I suspect they don't have a version 7.4. If you change that 7.4 to 7.3, it might work.
If there's something specific you need in PHP 7.4 or later, and this script was the only thing that worked, you might be out of luck unless you can use a container or VM locally. Something like this might get you unblocked.