Mesh between Fritzbox 7530 and archer c60v2

I have a Fritzbox 7530 with stock firmware and I want to use it as mesh master with the archer c60v2(openwrt) as slave.
Does anyone have already tried to do that?

The mesh on the stock firmware is proprietary and only compatible with other Fritz Box products.
To mesh with an OpenWrt box you will have to put OpenWrt firmware on the 7530.
It is then a simple matter of configuring 802.11s on both.

But don't use 19.07.4 as it is broken for IPQ40xx
Use 19.07.3 instead.

I can't flash openwrt on the Fritz box because it's given from my ISP and I have to give it back when I close my subscription.

Is there any way to make the archer c60 work as a repeater which device are connected in the subnet of the Fritzbox?
I can't make Google home devices work together if they're in different subnets