Back in the late transition days from PPC to Intel Apple had to eventually cut the rope for PPC. When early reports of developer beta builds of Snow Leopard surfaced, Apple neither clarified nor commented on the further PPC support of OS X beyond Leopard. But when the golden master was handed out it was clear — and communicated by then — that support for PPC was finally dropped. Things rested for years at that point (at least to my knowledge; Apple engineers knew better for sure). Then, mid-March 2020 I was hinted to a tweet by tesco@system2048 who posted a screenshot of a working SL-PPC

This information sourced from this MacRumors thread: https://forums.macrumors.com/threads/snow-leopard-on-unsupported-ppc-machines.2232031/
What ingredients are needed to start experimenting?

The easy way:

Below, the file PPC_SL_10A190.dmg is a bootable disk image of a system just after successful installation. Simply restore this image to a disk or partition using Disk Utility, and you can boot into the first time setup of a working Snow Leopard PPC install.

Note that you will need to select 'erase destination' when doing the restore from the DMG file to ensure that the image is properly bootable. For more information, watch the 6 minute video walkthrough of the process above.

The advanced way:

Obviously, a PowerPC machine is pre-requisite. A copy of a developer build of 10.6 (server or client) will be needed, in addition to a handful of original kernel extensions from 10.5.8, a USB drive (or even better, a firewire hard disk), and a helper system in form of a Mac capable of running 10.6 out-of-the box (e.g., MacBook 1,1 to 4,1, etc.).
In addition, if the installer of a server build is used, then at some point a license key will be needed to finalize the installation. The client versions, of course, never needed such keys.
Suitable Mac OS X Snow Leopard build(s)
The search currently goes on for intermediate PPC/Intel builds of Snow Leopard, but at present, the version proven to work are the builds 10A96 (server dev preview) and 10A190. There was probably a working build of 10A96 for clients, but this for now remains elusive (these would be labelled something like 'User DVD' or 'User Installer').
Between the 10A96 build and the “Golden Master”/GM (10A432) are several releases which we are looking for. If and when these become available for testing, we can check them for their PPC compatibility!

Generally, G4 and G5 machines capable of booting from external USB or Firewire drives should be able to install 10.6
Machines to be verified (that might or might not be able to boot/run 10.6 with additional tools or methods) are all G3 PowerMacs upgraded with G4 processors and/or required XPostFacto to running 10.4.x and/or 10.5.x in the first place. (exception: Pismo, see above). It may be also possible to add support for G4-upgraded PowerMac 8500s and other pre-G3 PowerMacs.
Macs with G3 (or lower) CPUs will most certainly be ruled out here (i.e. the original PowerBook G3 or iBook G3).

Initial patches to set up working installer media
Once you have created an installer (for now, this would be the 10A96 Server edition) on a bootable drive (either FireWire or USB for [PPCs which are able to boot from USB]), get the 10.6PPC archive and either use the script 10.6 PPC.sh (which you will need to adapt to your volume name prior to running it), or copy the kexts to the correct Extensions folder on your installer drive. Check and correct the file permissions to root/wheel xxx x-x x-x via chown/chmod terminal commands, or use the great handy tool, BatChmod.

This shell script will patch the installer to boot properly: https://github.com/julian-fairfax/osx-sl-patcher
Also, the file OSInstall.mpkg must be copied to /System/Installation/Packages (delete/replace original package there). Be sure to verify the file permissions for that, as well.
This is all best done with a more recent OS, but generally it should be feasible to do on a PPC running Leopard. (Have not tried this and done it on Catalina.)
If all is done right, then this installer volume should be bootable on G4/G5 machines!

Universal Binary

Emulating this? It should run fine under: QEMU