My dad ran a commercial 2-way radio business. There were multiple radios with programming software that would not work on anything above a 386 and DOS. He had a couple computers from the late-80s running for nearly 25 years, though I think he had to replace one of them with another of similar vintage. Also, had a 486 that he used for customer notes in WordPerfect up to about 2015.
I suspect he could have found a way to use a newer computer, but if it ain’t broke…
I still have a circa-1996 486 running Windows 95. It has an EPROM burner card and software that I use to reprogram the ECM in my car.
The cost of upgrading to modern software and hardware is substantial, plus the learning curve for something I only do rarely nowadays.
Intel was seling 386 CPU up until 2007. I personally was using brand new special equipment with 386 soldered to custom MBs with no VGA, serial only access. I suppose you can purchase such boards from ebay/recyclers today.