They aren’t forcing you to phase out your machine. They will continue to support it.
And third-parties will supply upgrades as the upgradable parts are roughly standard, so the Mac Pro is likely to be a completely usable machine for nearly a decade to come.
After that you’ll still get years on older MacOS, Linux, or Windows. Intel Macs can run both of the latter.
I kid, obviously. I've never seen anybody refer to the PowerPC as Motorola machines even though Motorola was part of the PowerPC alliance.