The FritzBox must see the client devices under class 1.1. While the MikroTik client must now see 10.3.1.1
/ip route
add dst-address=10.3.1.0/24 gateway=wireguard1 routing-table=main
the result
Well you need to confirm something.
What is the wireguard IP address of the fritz → ??
What is the subnet on the fritz trying to reach from MT -->??
I enabled routing on the Fritzbox server. Now, on the Mikrotik client, I can ping inside Winbox, but on Windows, the same router IP cannot be pinged.
Well you need to confirm something.
What is the wireguard IP address of the fritz → ??
What is the subnet on the fritz trying to reach from MT -->??
Hello dear, thank you for your patience first of all. Let me explain: I am in Milan as a client in Italy, while the Frizbox server is in Sicily, Catania. Currently, there are internet issues in your country, so my friend is in Cuba. Tomorrow I will provide more details; I have forwarded your information to him. Thank you very much; in the meantime, I have noticed that improvements have been made. Specifically, with the new route, the traffic, at least in Winbox, pings, and the traffic is high. The only thing missing is that on the PC, I receive the response to the IP of the router 10.3.1.1 from the Frizbox router class to reach it outside of Winbox. Thank you for your patience; see you tomorrow.
I understand sorry, time delay to get questions answered. I will try to be patient 
Hello dear, thank you very much, I solved the communication problem with the Fritzbox. The issue was on the client side; there was a Mikrotik Hex in between the main router with some pre-configured settings, causing connection problems with the client, even DHCP wasn’t working anymore. Today, I connected directly to the Huawei 5G router, using a regular switch instead of the Mikrotik Hex, with all the firewalls set up, and the result is that everything is working great. I can see Aruba ISP’s IP, so it’s working. Thank you very much for everything.
Hello dear, I tested better with DHCP and setting the IP class of my Mikrotik to 1.1, and WireGuard 2.1 with your configurations, everything works. The only thing I don’t understand is why I can ping from the Mikrotik to the Fritzbox, but not from the Fritzbox to my Mikrotik
Probably firewall rules on your MT router dont allow it.
The only rules I have in MikroTik are the ones you sent me. How is it possible? Can you tell me if I need to add
/ip firewall nat
add action=masquerade chain=srcnat out-interface-list=WAN
add action=masquerade chain=srcnat out-interface=wireguard1
Address wireguard:
192.168.2.1/24
Address dhcp client
192.168.88.1
Frizbox server
10.3.1.1/24
Answer:
Is it mandatory to put the IP in the WireGuard IP interface in ‘address’, or can it be avoided? Can it pick it up from the network card if I don’t put it? Do I need to put the IP with /32 instead of /24 by any chance?
Well not sure I can help further, the fact that the network was not as you were indicating tells me there is probably more at play here and thus its probably too difficult.
Ok thank you 