OK, what did I miss? What step absolutely requires fossil fuel?
If you think mining can be done with solar, then nothing. I take it you have never worked in serious industry.
Your list of things that can theoretically be done without fossil fuels is similar to list of what is necessary to live on Mars. Creating the check list isn't too tough. Doing it is nearly impossible, and totally impossible in the time frame necessary to avert disaster.
Let's start by recognizing that I did not say that mining could be done with solar. I said that mining can be done, and is being done with electricity.
Now, let's move past that and I'll claim, without hesitation, that mining could be done using only solar energy. We'd just need enough storage to allow mining to continue even when the Sun is not shining. Obviously solar-only is not the lowest cost way to power a renewable grid. It makes much more sense to add in a large percentage of wind along with whatever hydro, geothermal and other renewable sources we can put together.
"Doing it is nearly impossible"
You're not clear on what your "it" is. Running a large piece of equipment using electricity? Here's an entire gold mine that is run on electricity - no fossil fuel equipment used.
https://www.reuters.com/article/us-mining-electric-goldcorp/first-new-all-electric-mine-dumps-diesel-cuts-costs-pollution-idUSKBN1JH2FIRunning electric grids on 100% renewable energy? There are tons of research papers showing it can be done and around the world we see RE replacing fossil fuels.
"totally impossible in the time frame necessary to avert disaster"
I'm not sure how you define "disaster". If you mean avoiding damage caused by climate change we're already too late. We're already suffering disasters such as droughts, floods, heat waves, and wildfires. If you mean extreme climate change that would make it very difficult for humans to survive on planet Earth, we should be able to avoid that.
If we would simply put leaders in office who put a priority on fighting climate change we could be largely off fossil fuels in about 20 years.
Take the US grid. In 2016 we generated 65% of our electricity with fossil fuels. That fell to 63% in 2017. Electricity generated from renewable sources rose from 15% to 17%. We made a 2% market share transition in one year.
To get from 63% to 0% in 20 years we would need to annually flip 3.2% of our fossil fuel generation to renewable generation. We've already demonstrated that we can do 2% per year. And we did that without breaking a sweat. We wouldn't even need to double our generation efforts to achieve a 100% RE electricity supply by
2020.
Bad error. Should have been 2040.
Now vehicles. We already have EVs on our roads which are perfect replacements for ICEVs. They have the range, fast enough charging, and they are cheaper to power. What we would need to do is to build a lot of battery factories and open a bunch of lithium mines in a hurry but in less than ten years we could be manufacturing enough EVs to replace all ICEV manufacturing. And in another ten years or so most of the ICEVs that were manufactured earlier would be wearing out and disappearing.
These are things that we can do with the technology we have in hand right at this moment in time. We don't need to invent anything other than will to move us off fossil fuels in a couple of decades.
BTW, before you tell us that EVs are too expensive do you realize that if you bought a Tesla Model 3 or a Toyota Camry V6 that your monthly out of pocket expenses would be just about the same during a five year loan payoff? Long range luxury EVs are already price competitive with <luxury sedans.