Like the Ship of Theseus thought experiment, at what point does a thing no longer have sufficient continuity to its past to be called the same thing? [1]
Regardless, I have a hard time believing a 20 year old computer is "working like a champ". I've found the most people who say their <insert really old phone or computer> works perfectly have just gotten used to the slowness. Once they upgrade and try to go back for a day, they realize how wrong they were. Like how a 4k monitor looks "pretty good" to someone that uses a 1080p monitor everyday, but a 1080p monitor looks like "absolute unusable garbage" to someone who uses a 4k monitor everyday.
A typical "Upgradable" PC is in a box 10 times the size of the mini. If you upgrade the GPU on a PC, you toss out an older GPU because it has pretty much zero resale value. Typical Apple hardware is used for 10-15 years, often passing between multiple owners.
This is particularly true on the lower end where a 10 year old part is even interesting.