In an ideal world, I'd love to just make small gears, and gear shaped objects, as a job shop. There'd have to be some dealing with the internet for orders, shipping, etc.
First step would be bootstrapping up a CNC tool cutter, so I could cut hobs, and gear shaping cutters. Then the building of the CNC gear shapers and hobbing machines. Then onward to the finishing grinders, with superfinishing at minimum.
Small -- anything less than softball sized. Spur gears, helical gears, herringbone, straight bevel, splines, gear shaped objects like flow meter turbine blades, cams, etc. Stuff bigger than watch parts, but smaller than transmission parts.
I want to be able to make Collins antique radio gears, mostly. Stuff like the gear train in this Collins R/390/UUR receiver:
https://www.chavfreezone.me.uk/racal/2018/R390-Vs-RA17L.html
I still like things where I can prosper without internet presence or promotion.
But if having the internet would really help afterward that would be an additional win. I wouldn't want to count on it though.
However I was well accustomed to launching through high-touch efforts, I started my company a few years before the internet took off.
Didn't think it would be a good idea to become dependent at that point, and now looks like an even worse prospect :\
Everything was OK before email too, what I would miss the most is the "information superhighway" which was the main point of interest for the web to begin with in the 1990s.
For a couple of decades I did write plenty of code off and on when needed, especially before commercial offerings arrived.
Either way I think my final answer to the original question when it comes to both code and the internet is; when they are contributing to making a living it's from using the code and/or internet to run a better business, never making money by monetizing the code itself or through web promotion.
It's not that I'm looking for a business that doesn't need the internet, but I'm interested in if I can have a successful business without actively promoting the business on social media. I hate that in the modern age, it seems impossible or very difficult to promote your business without Meta platforms or running digital ads on social media (both Meta and non-Meta owned platforms).
So my question isn't really what business I could start without the internet, but rather if it's possible to run a successful business without running ads and creating promotional content on social media.
It makes me want to tear my skin that I need to do all this stuff on platforms that I hate. But, as one of my friends said, you can delegate the social media promotion of your business to other people, and if you don't use social media to promote your business you'll be left behind by your competitors who do.
Not an answer to your question, I know. Just sharing my frustration in what it seems you need to do to succeed... if I ever start a business.
That isn't universally true, though. If everyone is at the same skill level for a skill common enough to be a commodity, it is true. But if you do something unique or are just way better than other folks, you can succeed via referrals.