ERC-777 is a super updated version of ERC20. ERC777 is backwards compatible meaning that it has the same usability as ERC20, just many improvements on safety, functionality and so on. After ERC20 there was ERC223 which ORCA was meant to be, but we are moving with the times and improving every aspect of our project to the max, gotta stay with the best there is out there, so we moved to ERC777.
You can find clear comparisons on Google, just type in ERC223 vs ERC777
Cheers!