You can also just own it, cables are not inherently ugly. I’m not saying go full on Centre Pompidou, but a couple of dirt-cheap adhesive clips in an appropriate colour can go a long way (though not if your walls are plastered). The setup in 8-Bit Guy[1]’s old studio is a good inspiration.

(Sometimes the clips can be a bit too cheap, in which case tearing off the original crappy adhesive and using some of that insanely-strong double-sided 3M tape helps.)

[1] https://www.youtube.com/channel/UC8uT9cgJorJPWu7ITLGo9Ww

They are sharing their stories because they are more clever than the rest of us.

I had a cable going diagonally across the wall for ages before the SO put their foot down and demanded something slightly more aesthetically pleasing. Now it follows the trim at least.

I've imagined utility in making a crown molding be a c.a. 10cm angled piece with space behind, for just these reasons.

Held with screws of course, or otherwise removable and replaceable.

You can find crown molding with room for cables in it off the shelf, at least around here.

And if you don't want it to look especially great surface mounted trunking is decent enough and affordable. Actually it is very common here. Small rectangle mounted either to ceiling or floor of the wall.

Perhaps there’s a market for ethernet cables with LED wraps so you can run your cables near the ceiling AND have cool lighting effects in your house.

There's cable gutter kits you can probably get at your local DIY store to make that look a bit neater if you're looking to improve. They're usually stick-on so no drilling or anything required.

There's also decorative ones that run along your floor, I forgot the English name, but they're a bit bigger than the usual ones and can hold a number of cables out of sight.

You mean baseboards? Checking them is a good idea; some do have a space for running a cable. So if there's no need to go over a corner, it might be an option.