I had a Fritzbox 7581. The 5GHz could not connect to the FP3 or the FP2 of my friend.
Now I have a Fritzbox 7590 and the setting for the wifi channels is on automatic.
I get a very good signal on channel 100, so is the FP2. I am in Tilburg, the Netherlands.
I am on /e/. Didn’t have the Fritzbox 7590 when I was on orginal android.