According to the documentation (https://help.mikrotik.com/docs/display/ ... patibility),
the 2.4GHz interface of the RB4011iGS+5HacQ2HnD will be unusable after installing the wifiwave2 package.

I understand this is due to the chip not supporting it.
However, is it possible to make 5GHz work in wave2, while 2.4GHz works in the old wave1 mode at the same time?

No.

For this both drivers would have to be active at the same time and this is not supported (yet).

No.

For this both drivers would have to be active at the same time and this is not supported (yet).

Well, this is not good news. But still thanks for your reply!