If you want to install PHP 7.2, you’ll probably have to revert to Debian 9, yes. The
libcurl transition is a rather complex one and it’s impossible to mix and match
libcurl4-based packages; since Debian 10 uses
libcurl4, you need to use packages depending on that. (Ondrej may well provide Debian 10-compatible PHP 7.2 packages at some point, I don’t know what the plans are.)
On Debian 10, you should be able to install PHP 7.3,
php7.3-curl depends on
libcurl4. If you can’t, you’ve probably got conflicting repositories in your configuration; make sure you only attempt to install PHP packages from Debian itself.