Invalid file type "application/csv"

Your software
My Mautic version is: both 4.1.2 and 4.2
My PHP version is: 7.8
My Database type and version is: 5.7.37

Your problem
My problem is:
When I try to import a CSV I had this error in the UI:

Invalid file type “application/csv”. Use a file that matches one of the following mime types: “text/*”, “application/octet-stream”.

I have the same problem if I load a file that worked before and if I export a lot of contact and re-load it within mautic.

I don’t have it if I load a cvs file made from scratch.
I have the problem if I copy and paste the data from one file to another empty. I can’t understand…

I don’t have these problems if I load one of this files to other mautic instances

These errors are showing in the log:
mautic.WARNING: PHP Warning - Trying to access array offset on value of type bool - in file /…/app/bundles/PageBundle/Entity/HitRepository.php - at line 276

mautic.ERROR: Invalid clickthrough value: Yjo4Ontm…== {“exception”:"[object] (Mautic\CoreBundle\Exception\InvalidDecodedStringException(code: 0): The string b:8:{f:9:“fbhedf”;b:5:{v:3;f:8:“fzbvy”;v:4;v:742;}f:8:“fzbvy”;v:742;f:7:“fgbg”;f:55:“954a695862fdb926861964”;f:7:“yfbe”;f:9:“455425”;f:0:“dubaafy”;b:4:{f:8:“fzbvy”;v:742;}} is not a serialized array at /…/app/bundles/CoreBundle/Helper/ClickthroughHelper.php:46)"}

Solved:
The problem is with PHP 8.x. With PHP 7.4 all work fine