Now for php 7.4 it seems something changed and cannot install 7.4 this way.
Please anyone have good guide how to add php 7.4 from some trusted repo and not brake yum update in the future and will be installed in /opt as all other versions did?
Good question. I don’t think Remi will cause interference with the existing PHP 7.3, but since some CentOS repos have right-of-way (not sure about SCL), [edited here] it’s probably not an issue. But you could exclude PHP 7.3 in the remi-safe repo for extra peace of mind.
When PHP 7.3 or 7.4 updates are ready they’ll be updated from their respective repositories when you type yum update in a terminal or when Virtualmin has update notifications and fetches them. And Virtualmin should find and list any PHP installation regardless of where it came from. Or at least that’s my experience.