Like that time
Ars Technica took a Mac IIsi and found it really fun and useful when using it as it was meant to be used, compared to the time they tried to use
a TiBook as a modern internet machine.
If you can escape from the mindset that the only thing a computer is good for is to surf the internet and watch some YouTube videos, you can still use an old Mac quite capably, isolated from the rest of the internet-using earth. It's not hard to find good, old Macromedia and Adobe software that fills the Desktop Publishing, multimedia and digital imaging niches. Gifs and Jpegs just haven't changed much in the past 20 years.
How about a DAW for music making? Mac OS 9 could do that, so could an old school Amiga. I mean that's the whole point of MacOS9Lives really. Old machines that didn't have so many background processes swimming in the background could be shockingly effective at producing digital music, given strict timings that can't be as easily done in a multithreaded environment and the trusty MIDI protocol.
Some niches like digital video are going to need a multicore Intel Mac
or even an iPhone. That's still a fraction of the content we make and consume every day.
One time, I used to have an iPad (first gen!) along with a Quadra 800 for games and document writings, and that was how I was getting by with the internet/music split on the iPad with real writing work and classic games on the Quadra. Clumsy, but fun, and it kept me from being bombarded by modern life.
That setup's still perfectly fine now. You just need to take that internet and put it in a (gasp) Chromebook, or an iPad. Or some other dedicated device that's made for consumption.