Serious debugging

After launching sudo /sbin/wpa_supplicant -d -c/etc/wpa_supplicant/wpa_supplicant-wlan0.conf -Dnl80211,wext -iwlan0 I got

https://pastebin.com/nBkm3SNx

For the joy of a commenter

For the joy of a commenter I am posting the result of the following command

pi@raspberrypi:~ $ sudo iw wlan0 

The result is incredibly long and I personally doubt that it works with systemd-networkd. Here it is: https://pastebin.com/h6r46mB8

Check on DHCP (as apparently is a known issue, see second link)

Launching journalctl -b -u systemd-networkd, I have tried to reconnect several times with my android devices From 12:16 on, however I see only two DHCP server requests.

I found out that in order to download updates faster it was convenient to switch off RasPi Ipv6. Could this interfere? I had this doubt since when I connected to the network from a windows machine I found out in the WiFi properties that there is a Link-local IPv6 address. Since it is often claimed that Link-local is what is not supported in android, it might be that the Ipv6 settings are necessary for android to connect to a wifi network. But how to switch on IPv6 and set DHCP inside systemd-networkd?

I got that "So somehow, having Multicast / Broadcast on my network kicks my Android devices". I don't even know how to chekc if my hotspot has those or can avoid those.

In partucular the comment "This page has a wealth of information about which IP to use as per your needs. " reminds me of a similar comment in an answer at the link under the section "another similar question" however the link does not seem to help.

However I still can not connect from my smartphones.

Check on DHCP (as apparently is a known issue, see the second link)

Launching journalctl -b -u systemd-networkd, I have tried to reconnect several times with my android devices From 12:16 on, however, I see only two DHCP server requests.

I found out that in order to download updates faster it was convenient to switch off RasPi Ipv6. Could this interfere? I had this doubt since when I connected to the network from a Windows machine I found out in the WiFi properties that there is a Link-local IPv6 address. Since it is often claimed that Link-local is what is not supported in android, it might be that the Ipv6 settings are necessary for android to connect to a wifi network. But how to switch on IPv6 and set DHCP inside systemd-networkd?

I got that "So somehow, having Multicast / Broadcast on my network kicks my Android devices". I don't even know how to check if my hotspot has those or can avoid those.

In particular the comment "This page has a wealth of information about which IP to use as per your needs. " reminds me of a similar comment in an answer at the link under the section "another similar question" however the link does not seem to help.

However, I still can not connect from my smartphones.