All these multi php selector in cpanel server have only one option to set the php version on per user base. You can’t chose php versions of individual websites under one cpanel user. So in effect the cpanel users are only using one version of PHP at a time. That is not something multi php aims to. Even those options not using php-fpm too.
How can I solve this ?
You need to install the cpnginx 10 plugin in cpanel. It use multiple php-fpms provided by cpanel on per domain or website base. So every user in your cpanel user can select any version of php for his individual websites . Also cpnginx use php-fpm too.