@0xDEADBEEF If I'm not mistaken, @ParadeGrotesque might be able to help you with that. He recently installed QEMU 9.0.0 on Slackware.
Side note: I have 3 VMs running on my server at all times: NetBSD, OpenBSD and Debian. Uptime is measured in weeks or more. Uptime of the Slackware server is about 70+ days right now.
I also run a Slackware 15 VM, but this one I only switch on from time to time.
VNC also works and it is possible to both SSH and VNC into VMs with this setup.
@josemanuel @0xDEADBEEF
KVM is in the stock "huge" kernel on Slackware.
Compiling qemu 9.0.0 on Slackware 15 is just a matter of running "./configure ; make ; make install" and it compiles everything.
The only dependency of qemu is libslirp if you want user mode networking, that you can get from: https://gitlab.freedesktop.org/slirp/libslirp
Again, compiling libslirp is just a matter of "./configure ; make ; make install".
Run your VMs with '-accel kvm' and you should be OK.
Hope this helps!