Hi,
I have manged to install php 5.6 in centos 8 using remi repo. Below are the steps which I have followed.
1. Install remi repo in centos 8
2. Install php 5.6 and its required modules
3. Register the php.56 fcgi module with php, If all good you will get handler id and successfully registered message.
View attachment 20685
5. You can verify it using the below command
View attachment 20686
6. Now the php version will be listed in front end of plesk in php version drop down
View attachment 20687