With each new OS version, Apple eliminates support for older hardware, even if it's still capable of running the new OS.
Planned obsolescence or just a push for you to make an upgrade? It doesn't matter, actually, as there are still ways to use the newest OS on older Apple computers, such as:
Early-2008 (or newer) Mac Pro, iMac, or MacBook ProLate-2009 (or newer) MacBook Air or unibody MacBookEarly-2009 (or newer) Mac Mini or white MacBook
Create a New Virtual Machine. After finishing the steps above, now it’s time to begin start. Mac Os X Mojave Dmg Install macOS Mojave on unsupported Mac. Before going to upgrade there are two important points that you should know about that, the first one checks your Wifi compatibility, because some of Mac have Wifi which is unsupported in the macOS Mojave.
What do you need?
How To Install Sierra On Unsupported Mac
1. An 8Gb or bigger USB memory stick2. MacOS Sierra Patcher for Mac - it will create a custom USB installation3. MacOS Sierra installation App4. AUSEnabler - it will help you get future software updates on your installation.
For known issues, read here.
Steps:
Install Catalina On Unsupported Mac
1. Go to Spotlight - System Information - Hardware Overview - Model Identifier and note the value. In my case was MacBook5,1
2. You need Install macOS Sierra.app in your Applications Folder.
You can get this from a newer (supported system), from a friend or if you have a supported computer.
3. Run MacOS Sierra Patcher for Mac and, using the 8Gb+ USB memory stick, create a custom bootable installation kit.
4. When the creation of the tool is finished, reboot the computer, keep ALT/OPT key pressed, and select the USB device on boot.
5. Install MacOS as usual and wait for the process to finish.It will restart, but will not work, so you need to repeat the step 4 and boot from the USB drive, to run post installation tweaks.
In the first interface after boot, select from the top menu: Utilities - MacOS Post Install
Now, you must select the correct Model Identifier for your hardware (see Step 1) and apply the suggested tweaks and reboot!
6. Use AUSEnabler to get software updates.
That's it!