AVR Native (non-blocking) driver now supports up to 8 I2C Multiplexers, as does any controller that uses Wire for I2C.
Other native drivers will be updated in due course.
Following on from the change to I2CManager_SAMD.h, the capability of deferring a request to change the speed of the I2C has been removed from the SAMD driver and put into the common NonBlocking code, so that all native drivers benefit from it.
The speed change is deferred until the next transmission is about to start to avoid issues with the I2C module being disabled and enabled during a transmission.