This is not a fiber optic problem (what kind of contract do you have?), but exclusively a WLAN issue. The problem could be the FRITZ!Box or its placement.
We also have the 7590 and no reception directly on the 1st floor. The concrete ceilings, steel, and underfloor heating are not very conducive to Wi-Fi.
Therefore, one should actually plan access points at critical points in the house during new construction.
Internet connection
IPv4: connected since 20.11.2020, 14:57, Telekom, speed of the internet access (available bitrate): ↓61.8 Mbit/s ↑12.4 Mbit/s
IPv6: connected since 20.11.2020, 14:57, Telekom, speed of the internet access (available bitrate): ↓61.8 Mbit/s ↑12.4 Mbit/s
Test internet connection speed?
I will test tomorrow what arrives and try today to switch the phones to the 5 GHz instead of the 2.4 GHz network. That should bring some improvement, right?
If these are definitely the key data of the FritzBox for the connection and you have fiber with a DL 250+ tariff, then this is definitely not a WLAN problem.
Which does not exclude that you still have one. Depending on the circumstances, walls, refrigerators, mirrors, plants, you can have massive reception losses even at 2 meters.
So if you want to solve it quickly, turn off the Wi-Fi on the Fritzbox and use a Xiaomi ac2100 router and configure it as a Wi-Fi router, that thing has a really good transmission power somewhere around 2000Mbps.