Darkle Many of the new syntax features introduced with PHP8 are not yet available to us because we need to be compatible with older versions of PHP. I suppose there's the standard array of security and performance tweaks that comes with any language update? Also there's a JIT compiler but we haven't done any benchmarking to test its effects yet.
As to general improvements, you can follow our development roadmap via the github milestone: https://github.com/flarum/core/milestone/20
