with macOS Catalina 10.15 update Apple decided to remove some of the lineups from its list for the new update because most of them are either unusable or have a lack of resources for macOS Catalina.

Early-2008 or newer Mac Pro, iMac, or MacBook Pro
iMac11,x (systems with AMD Radeon HD 5xxx and 6xxx series GPUs will be almost unusable due to the lack of acceleration)
iMac12,x (systems with AMD Radeon HD 5xxx and 6xxx series GPUs will be almost unusable due to the lack of acceleration)

Late-2008 or newer MacBook Air or Aluminum Unibody MacBook

Early-2009 or newer Mac Mini or white MacBook

Early-2008 or newer Xserve

Catalina Builds and Installer Versions

2019/06/04 10.15.0 beta 1, build 19A471t, installer 15.0.11
2019/06/17 10.15.0 beta 2, build 19A487l, installer 15.0.15
2019/07/02 10.15.0 beta 3, build 19A501i, installer 15.0.17
2019/07/16 10.15.0 beta 4, build 19A512f, installer 15.0.18
2019/07/31 10.15.0 beta 5, build 19A526h, installer 15.0.21
2019/08/19 10.15.0 beta 6, build 19A536g, installer 15.0.23
2019/08/28 10.15.0 beta 7, build 19A546d, installer 15.0.25
2019/09/10 10.15.0 beta 8, build 19A558d, installer 15.0.27
2019/09/23 10.15.0 beta 9, build 19A573a, installer 15.0.30
2019/09/30 10.15.0 beta 10, build 19A578c, installer 15.0.31

Essentially the Catalina Patcher Tool creates a modified USB installer drive (similar to the regular Catalina boot installer drive you can make) which you can then use to install not only macOS Mojave on the otherwise unsupported Macs listed below, but also a series of patched macOS Mojave component files that allow it to boot.

Just a quick word of caution: while you may be able to get macOS Mojave running on an unsupported Mac, this is true only for advanced users who are adventurous. You certainly wouldn’t want to try this on a Mac that you must have to perform in an optimal setting at all times, or on your only computer, but if you feel like tinkering around and running macOS Mojave on an unsupported Macintosh computer you can certainly try it out. Because it patches the operating system and installer, not everything is going to work perfectly on all machines — for example, on some machines networking may not work, or an iSight camera may not work, or GPU acceleration may not function — and there could be various bugs, performance quirks, and other theoretical problems with attempting this, but for the truly tech-savvy and brave, the Mojave patcher tool and accompanying walkthrough from DosDude can get the job done.

The DosDude website has both a complete tutorial available at the above link, along with the downloadable patcher tool.

OR you can also make an entirely new Hackintosh for yourself.

[GUIDE] Is It Possible To Make A $400 Build Hackintosh in 2020