@j_watson The error message is pretty straightforward. Your Composer file has declared the project needs a version of PHP greater than 7.4, and you’re running it in an environment that has a lower version.
@martinbean I have. There are some discussions online but no clear fixes. I've been using the same version but I think my host may be using a newer version.
@j_watson Stop saying “there are no clear fixes”. The error message is clear (you’re trying to install packages using an older version of PHP that’s been declared) and the solution to that is also clear: use a version of PHP that’s greater than 7.4.
As @martinbean said, the error message is pretty self-explanatory.
With regards to steps to fixing it - there's no set of commands that works on all systems. So we can't just give you some code to make the error disappear.
Depending on what your Operating System/Development Environment is... use Google to find instructions on installing/updating PHP (e.g. How To Update PHP on Ubuntu 18.04).
There's a ton of articles out there to help you through that process!