I found the following answer in a topic on a forum:
For full text look at: https://github.com/PrestaShop/PrestaShop/issues/16477
But in short below:
The main issue we have right now is that PHP is evolving too fast and with too much breaking changes between minor versions. The changes being introduced between php7.2, php7.3 and php7.4 require a huge amount of time and energy to be handled correctly on PrestaShop side, and our current team size only allows us to provide this amount of time and energy once per version of PHP and version of PrestaShop.
So we have
PS 1.7.6 compatible with php7.2
PS 1.7.7 compatible with php7.3
PS 1.7.8 compatible with php7.4
And it might become worse with php8.
Release out now is Prestashop 1.7.6.8, so the provider should create a temporary fix to PHP 7.2 to fix a lot of problems.