Homebrew users:
This can happen simply because your php version is not linked.
Goto /usr/local/Cellar, list out the content and see what versions of php you have installed. You should see directories and symlinks as so:
lrwxr-xr-x 1 kazajhodo admin 7 May 22 2019 php72 -> php@7.2
lrwxr-xr-x 1 kazajhodo admin 7 Feb 26 2020 php73 -> php@7.3
lrwxr-xr-x 1 kazajhodo admin 7 Jun 12 2020 php74 -> php@7.4
lrwxr-xr-x 1 kazajhodo admin 7 Jan 22 2021 php80 -> php@8.0
lrwxr-xr-x 1 kazajhodo admin 7 Jan 4 11:58 php81 -> php@8.1
drwxr-xr-x 3 kazajhodo staff 96 Jan 4 11:34 php@7.2
drwxr-xr-x 3 kazajhodo staff 96 Aug 8 19:32 php@7.3
drwxr-xr-x 4 kazajhodo staff 128 Jan 4 11:55 php@7.4
lrwxr-xr-x 1 kazajhodo admin 18 Jan 22 2021 php@8.0 -> /usr/local/bin/php
lrwxr-xr-x 1 kazajhodo admin 18 Jan 4 11:58 php@8.1 -> /usr/local/bin/php
If the version you want is there, you can link it with brew link php@7.4
.
Then your bash should have php defined.
Installing php again will also work, because it will add the symlink in the install process; but you only likely actually need the symlink.