* R functions that users write that use functions that Arrow supports in dataset queries now can be used in queries too. Previously, only functions that used arithmetic operators worked. For example, `time_hours <- function(mins) mins / 60` worked, but `time_hours_rounded <- function(mins) round(mins / 60)` did not; now both work. These are automatic translations rather than true user-defined functions (UDFs); for UDFs, see `register_scalar_function()`. (#41223)

* `summarize()` supports more complex expressions, and correctly handles cases where column names are reused in expressions.

* The `na_matches` argument to the `dplyr::*_join()` functions is now supported. This argument controls whether `NA` values are considered equal when joining. (#41358)