The cost is per transaction, not per amount transferred. A small transaction takes just as much space in the ledger as a large transaction.

A fun thought experiment is to see just how limited the throughput of Bitcoin is. Suppose the Bitcoin enthusiasts were to get their wish and Bitcoin becomes the dominant "currency". If every person on the planet were to make a bitcoin transaction once if their lifetime, that alone would be too many transactions/second for the network to handle.

Sounds like a single bitcoin transaction is like transferring a few billion dollars at a time.

Pretty much. It is only useful in cases where you are making very large transactions. At that point, you have few enough actors that setting up a trusted network is far, far cheaper and more flexible. The trustless nature of Bitcoin is what makes it unscalable.

Its not correct. The network spends this energy either ways, and it not only allows transactions to happen but it is integral to securing funds that are not moving. Dividing the energy consumption by number of transactions is therefore nonsense.

Bitcoin transaction value has nothing to do with it's energy consumption. So moving a cent or a million both cost the same.

The power usage is the same if you transfer $100 worth of BTC or $100 billion.

What happens if a few millions people send 5 bucks worth of bitcoin? A global power outage?

Depends on the transaction fees associated with those transfers. If those millions of people also post higher-than-average transaction fees, then the Bitcoin network prioritizes those payments, and cannot process any other transfers.

They would have to wait a lot. Also a fee is almost $20 now. So they would make a bad and slow deal.

That seems like a natural rate limiter that would prevent wasting any meaningful amount of energy on bitcoin.

That transaction fee will be used to run more miners and thus increase the energy usage.

Higher fees means fewer transactions. Nobody's going to buy a $3 coffee with $300 fees just because it's bitcoin.

Nobody will pay a coffee with BTC, just like you don't pay for your stuff with a gold coins.

Some say Litecoin will be used for that but I doubt it. Coins like Cardano or IOTA will be used for transactions. I'm not sure about Cardano but with IOTA you can transfer a fraction of a cent (or no value at all) without fees (that doesn't mean everything will be always fee-less).