We already have a "third party" now in the sense the GOP is unrecognizable from 20 years ago; the old GOP died out, like the Whig Party.
As a Brazilian, I think it's unfortunately more likely than you think. Here in Brazil, we got a completely rewritten constitution (the 1988 constitution) after our USA-backed military dictatorship ended. So if the current USA government becomes a dictatorship (which unfortunately does not seem unlikely enough right now), there's a good chance the USA will also get a brand new constitution after all that mess ends, hopefully one with better electoral mechanics.
That's not always true. Proportional representation in the House would help a lot, and that could be done by passing a regular law. (The current "one member per district" law is only from 1967: [0])
[0]: https://act.represent.us/sign/proportional-representation/
The only way that can happen is if several red state legislatures agree to the Compact. This Compact is useless to replacing the Electoral College if only blue states sign up; these states would have voted blue in an election, anyway. It tips over to 270 if several red states sign up and allocate their electoral votes against the wishes of their own red state constituencies. Would that be democratic? It is obvious why the growth of the compact has stalled at 209 votes; it is irrational for a red state to join it. It is also true in the mirror image if it were a "red state 270 vote compact," no blue state would join it.
It is more possible now than ever though with unprecedented communication. But to paraphrase Warren Buffet a bit: "We (the rich) are a lot better at this and we're kicking your ass right now". Imagine if we could have even a fraction of the youth anger from Tiktok aimed at such issues above.