Any application can add whatever process management ( init ) configuration they want to. That's why it seems rediculous to have an OS that only supports one.
Lets say I'm only using SysVInit for example, and then I install a 3rd party application. ( one that isn't in my distro's repo's by default ) Something like elasticsearch for example. So I add the elasticsearch repo to my list of repos.
Then I run apt or dnf install elasticsearch.
Guess what, it doesn't matter if every thing else runs under sysV rc.init files or not. The application is going to install a systemd service file whether I want it to or not. Almost all ( I would guess 95% or more ) of the applications I install via 3rd party repo's are going to install systemd service files by default.
Now if my system truly doesn't support systemd. I can always write a rc.init file to start and stop my application.
But if it turns the application is running in the background, then that proves that my systems does indeed support
systemd. Whether I thought it did or not.
Perhaps installing MX sysV version, simply means all the service files are of rc.init type?
To view all services using sysV ( rc.nit )
Just type...
chkconfig
or
chkconfig --list
To view all services using systemd.
systemctl list-unit-files
If items show up in both lists, your system supports both systemd and sysVinit.
Note: My Fedora39 system does not support chkconfig by default.
However I do see, that I can install it if I want to.