Same solution I’ve been peddling for years.
1. Everything is challengeable and coaches only get two the entire game. No getting a third if you win two, just two total.
2. Plays are reviewed in real time. If it isn’t obvious in real time, it isn’t obvious.
3. There is a “shot clock” of 2-3 minutes. If there isn’t a reversal by then, the call on the field stands.