I love the idea of terraforming Mars, to the point of spending a lot of time understanding the challenges to achieving success.

Conceptually there is always tech which we are yet to discover, but that just pushes the conversation into hand wavy territory, and discussing the details is always more fun.

The simplest plans are to start a runaway green house effect, in order to warm the planet up.

That alone requires signficant but potentially achievable feats of engineering.

But as I remember, the unsolved issue remains in maintaining a stable atmosphere, one which isnt sheared away by solar wind.

This is why the tidal locking issue is the problem. The core is solid on Mars, and the idea of spinning up a planet to rotate puts us beyond space elevator tech and nearing solar engineering levels of ambition.

As someone else suggested, there's the idea of having a super conducting magnet on the equator to create the field.

That's still below solar engineering, but a feat of such magnitude that underground habs win out as an option for the foreseeable future.