What determines price of Bitcoin and what determines the transaction fee? When Bitcoins reach their total, how will transaction fees be kept reasonable for use?

Hello I’m trying to learn more about Bitcoin and cryptocurrency in general. I watched a YouTube video and it got moe wondering a few things.

When all Bitcoins have been mined, then it is only transaction fees that will be paid to miners. In that case, the transaction fees would have to increase? Otherwise why would anyone mine? Or would there be other ways for miners to get a return? Or would there be self-sustainable mining (e.g. using solar) set up running automatically across the world that doesn’t generate a return.

If transaction fees are too high, does that then limit the use of Bitcoin? The value of anything is determined by what people view it to be worth, and if the use of Bitcoin is limited, would value of Bitcoin then fall, and could that lead to the whole Bitcoin project collapsing?

I just don’t see how it can continue to be feasible in the very long term.

Would love to hear any discussion about Bitcoin in the very long term.