Is there a way to run old mac applications in mac os 10.14?

You could repurpose, or add an SSD drive, and install the version of OS X, or macOS that supports your games. Then alternate boot when you want to play those older games. You cannot install a version of the operating system older than that which was originally shipped on the Mac Pro.

The game developers are entirely responsible for keeping their software current as new versions of the operating system arrive. If they have not done that, you cannot make incompatible applications work on Mojave, hence rather than downgrading Mojave, I suggest the first paragraph.

Another alternative is to install a VM environment such as VirtualBox, which is free. You can then install whatever version of macOS you want in VirtualBox, and then install your games there. That way, there would be no need to reboot your machine each time that you want to play your games.

For the record, I used to run VirtualBox on my El Capitan iMac. In VirtualBox, I ran Mountain Lion, so that I could run SheepShaver. And in SheepShaver, I ran OS 9.0.4, so that I could run my Hermes II BBS. It was quite a convoluted setup, but it worked perfectly, until I finally shut down my BBS permanently a few years ago.

See this thread in the VirtualBox forums.

https://forums.virtualbox.org/viewtopic.php?f=22&t=81443

one thing you needs to consider playing games in a virtual machine is that a virtual machine does not have access to any 3d features of a video card, so it will be a baseline generic video card adaptor. which games expecting a 3d accelrated video card would not view as meeting the requirements.

Not necessarily. If they installed just fine, then don't worry about it. What I was referring to was the fact that in previous months -- they may have possibly stopped the practice by now due to the backlash -- they would create their own small installers, which to my recollection, did not contain the actual installer for the app. You had to run that little installer, in order to get the actual app installer, and that is when they would insert the adware. If what you downloaded were the actual full-sized installers, as created by the developers, then as I said, you should be okay.

that a virtual machine would never be able to access any sort of 3d gpu power internal or external

it is the nature of virtual machines

the fact you can have 2 side by side in windows is the give away

depend on how old and what games as in if they are rosetta

FWIW, I posted a message about the security warnings on the VirtualBox forum.