Your requirements could not be resolved to an installable set of packages.

Problems : Your requirements could not be resolved to an installable set of packages.

Solution : 

Run this command:

composer install --ignore-platform-reqs

or

composer update --ignore-platform-reqs

Solution 2nd 

I solved the same issue setting 'laravel/framework' dependency version from "^8.0" to "^7.0".

After that running 

 "composer update --ignore-platform-reqs"  simply worked