$11 billion stock buy back in the last quarter (Q3), and cash in bank still rose from $33bn to $38bn
(By comparison Apple has about $56bn cash after debt is taken into account).

So either Nvidia thinks its' share price will go a lot higher and it'll be a wise investment - giving shareholders added value - or it can't think what to do with cash / can't get a good enough return if it uses it itself.

Am I missing something?
Thoughts?

I consider buying backs on such highly rated shares as highly dodgy. They are basically buying shares to issue to staff. Instead of creating new shares. It's a way of hiding just how overpaid the management are. Much more prevalent in the US than the UK.
If instead they created new shares it would result in a much reduced earnings per share increase, possibly a decrease. They are hiding the management pay.

True but the FCF of Nvidia is not great in comparison to the likes of boring stuff like SPGI, FICO Netflix.
Then as you point out - there is the unpredictability element.
The current share price is bit more about hype and potential rather than FCF. A big chunk of revenue is going to pay stock based comp - why they trail the SPGI's, NFLX etc.
However their investments in the likes of ARM gives them some power
Then there is other investments such as SOUND, SERV - have shot to the moon.
Finally you have the recent announcement re tie up with TSLA which further boosts their potential.
Overall their current dominance in chips may become their weak point and may lead them to become an incubator for AI companies and, like Amazon they will just chew up competition (like the ARM stake).
For all of these they need access to cash.
So whilst Buybacks id dodgy accounting to keep share price afloat and high, they can use it later down the line.

Under the bonnet for this piece of business - Nvidia relies on usage of third party who use another third party and they all share the revenue - whilst this is good in the short term.
Open AI already has a desire to create chips themselves with the likes of TMSC and Broadcom (not NVIDIA) - how long does that income last ?

Consider the notion that - someone like GOOG has its own AI model but not the chips - Nvidia;s income is primarily a chip supplier.

Now consider someone like Broadcom who is now focusing on helping companies ( such as Open AI), and others like say GOOG, develop chips. Now GOOG has its own Chips and AI model also and does not need ChatGPT.

Now Nvidia's advantage of being a chip manufacturer has fallen away - there was no MOAT around it. It's success was reliant on a third party. Look at Intel and Apple.

So Nvidia needs to do a Amazon, Facebook and Google - diversify and invest - which it is doing - being an investor and incubator of AI companies.

The Tesla tie up should give it legs to run (along with the ARM investment) - - so make hay while the sun is shining.

In fact institutional investors are piling into TSLA at inflated prices as they have now come to the realisation that it is not a car company (which many retail investors have been saying) but an AI company. The electric car race was a diversion. The new race which it is likely to win is the Robotic race (which the likes of Honda and Sony started back in the 90's but treated as a game)