Sometimes you can ignore the ICU check. In my case, I have prestashop 1.7.6.1 and the required ICU is 64.1 but I have ICU 64.2 (the latest). Prestashop doesn't check greater version. I dont think I should downgrade my ICU. I think this should be considered a bug. PHP version came bundled with its own ICU's version.
Edited:
I think the best way to check system requirement is to use this recommended tool by Prestashop: https://github.com/PrestaShop/php-ps-info/releases
This tool is recommended by Prestashop as mentioned in the official documentation: https://devdocs.prestashop.com/1.7/basics/installation/system-requirements/