I know about IRC, but I am against using it, in principle. It never worked for me in the past anyway.
Maybe you want to tell me something which you cannot share in the public, but I'd like to rely only on the information that is available publicly. Otherwise I don't see how IRC can be more useful or effective, compared to other means of communication. With email you have at least the opportunity to answer months later (after your vacations are over).
Maybe this can be a good project for GSoC. Debian participates there regularly, so it is almost guaranteed that this project would be accepted.
As a workaround, is it possible to install in debian-edu the php7.4, instead of the latest one (or besides it)? This would allow GOsa to work, until it is fixed.
I have to install many web applications on my server and they all have conflicting requirements about the tools that they use and their versions (for example one of them needs php7.4 and another needs php8.x). For this reason I install each of them in a Docker container, so that they can be isolated from each-other, and they don't step on the toes of each-other.
I am not sure whether using Docker containers in DebianEdu is an option. If it was, I might try to containerize GOsa, so that its old dependencies don't affect the rest of the system.