I think the sweet spot was people growing up in the time that their early experience spanned the DOS & 8-bit era into the ubiquity of GUIs (say mid-1980s to mid-1990s), which may reflect my own familiarity bias though I was technically a little earlier than that.

I'll second that. Saw some early PC and even wrote a basic Basic program in, must have been math class in the gymnasium (~"high school", class 10-12), but really started using computers at university in 1985 -- first a minicomputer with TTY (and even some printing!) terminals in 1985, then PCs a year or so later. First with a colourful menu system (Press 1 for DisplayWriter, 2 for MINITAB, etc) [1], then Windows 3 a year or so after that.

My son, recently of age, has no fucking idea about anything beneath the GUI. OTOH, my somewhat older stepson is a games and recently "full stack" -- which has something to do with tis newfangled Web thingy, I think -- programmer. (OTGH, fuck knows what he knows of anything beneath Unity and React...)

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[1]: That is, press a number and then [Enter]. This, I later (after some rudimentary hints on DOS from a classmate) found out, called the batch files 1.BAT, 2.BAT, etc, which in turn set up whatever needed to be set up and then started the respective application.

Determining the sweet spot is a fun thought. I'd argue for the Windows 7 era. General purpose computing is still the norm. The web & apps have almost as many services as now, but with less bloat and less tracking. There's social media but it's not completely dominant. Linux for desktop is beginning to be in good shape. Smartphones are available for those who want them but they're not dominant yet either.

That's my personal one. I'm sure it'll be different for everyone else.

Windows 7 was the first time I installed a Windows OS and didn't have to custom install a bunch of drivers, it was all just done for me.

I doubt most people, with the exception of builders of custom rigs, even know that a driver is a thing.

I worked at a computer helpdesk in college during this time. Cleaning up malware transmitted via email, IE6 and AIM made up the lion's share of my work.

In my experience, students understood computers a LOT better after being told that their term paper is not recoverable from their busted HDD, and that they should be saving their work on the network drive in future.

I think it was before that to be honest. I grew up in that era and gui mentality was tough to overcome. The cli was a black box for me for years. Once I learned bash I felt like I knew exactly how a computer worked and how a text file could turn into a 3d video game. Before that it was black magic.

GUI computers still lets you do all of that though. The main damage the switch to smartphones has is that they severely limit what you are allowed to do with your computer, you cannot properly tinker with them even if you want to.