The following PHP extensions are required but are not installed

I’m beginner, I got this error I try to fix it many times but it won’t.
I tried the recommendation to go in php.ini then uncomment the ‘extension=mbstring’
and
‘extension=openssl’
(https://i.sstatic.net/eA4PhoLv.png)

enter image description here

Do you have any idea how to fix it?

I tried to follow the php.ini file but it doesn’t work