Downgrading 10.6 to 10.4

Some 10.4.4 systems (Tiger) can be upgraded all the way to 10.11.6 (El Capitan), or downgraded.

If 10.4.4 to 10.4.11 Tiger is your intent to use, you must find the original 10.4 installer disk that came with the Mac in question, and wipe the hard drive with Disk Utility after using the Option key to boot that disk.

It will have the make and model year on the disk.

The combo 10.4.11 installer for Intel will upgrade your 10.4 to 10.4.11. You can't use the PowerPC versions of 10.4 on Intel Macs, which all 10.6 installed Macs are.

If your intent is to downgrade from 10.15.7 Catalina to 10.14.6 Mojave, you and your Mac is older than the October 2019 release of Catalina, you can either use internet recovery to install Mojave on a separate partition, or an erased drive from Disk Utility in internet recovery. For downgrade instructions of that variety, see this tip. As Eau says, no Mac may run a Mac OS older than it shipped with.

What exactly do you want to do.

The title asks how to downgrade from Mac OS X Snow Leopard 10.6 to Mac OS X Tiger 10.4.

And your question now asks how to downgrade from macOS 10.15.7 Catalina to Mac OS X Tiger 10.14.

Can you clarify exactly what you want help on.

And just so you know there is no way a mac that is running macOS Catalina 10.15.7 can ever be downgraded

to run Mac OS X 10.4 Tiger.

Macs cannot run an OS older than the one they came preinstalled with.

No usable MacBook Pro supported OS X Tiger that supports macOS Catalina. If you are on Snow Leopard, backup you data first using time machine and install a copy of Tiger and copy it to a USB drive, boot into that, erase the disk using Disk Utility, proceed to the setup and you're good to go.