We have the tech (you're almost certainly already using it), we have not deployed it at sufficient scale yet.
But we are building the factories to make the batteries, and the mines to feed the factories, as fast as we can raise money to do so.
I'm not sure what's happening with hydrogen (apparently it's much cheaper than batteries?); but regardless, that technology predates all forms of generating electricity more complex than the etymological origin of the word (ἤλεκτρον, amber) — "rubbing things together" was the only option when Deimand and van Troostwijk charged their Leyden jar back in 1789 and demonstrated electrolysis.
It's fine to say "the factories need to be built", as long as they can be built at a manageable price. But price is a huge factor that cannot be ignored, and it's high enough in this situation to make the word "trivial" incorrect.
No new problems need to be solved, so in that sense it is trivial.
It costs a lot of money in absolute terms, so in that sense it is not trivial.
The cost (for global battery based storage, the most expensive serious storage option) is in the order of 6 months global supply of crude oil to turn rocks into batteries (i.e. the dumbest possible limit on the cost of recycling), those batteries last at least three years even using the worst cycle-count estimates I've seen and throwing the batteries away at 70% of initial peak capacity, that's trivial.
Opening new mines and factories, even if the new mines provide new work for workers currently in fossil fuels, may be a significant geopolitical and economic shift, so in that sense it isn't trivial.
And so on.
For hydrogen, it's "build a tank that only leaks a little bit". (We'd probably be better off adding some carbon to that hydrogen, but I have no idea if anyone is working on that at sufficient scale even though the tech is over a century old).
Factories for any form of storage are not different in any material way from a thousand other factories we know work. We have been making factories for going on three centuries, and know we can. Making and operating factories is expensive capex, but exploring, extracting, transporting, and refining fossil fuels is an even more expensive opex. If we could afford fossil opex, renewable capex of similar order is strictly better.
Variability is in fact a trivial problem solved by storage and transportable backup. Even NG suffices as backup. Even coal suffices as backup. In the future, ammonia will take up that role.