Ther router has multiple dhcp servers. Ethernet connections will get IP from router`s DHCP server (dhcp3) in range 192.168.90.2 to 192.168.90.254 where gateway will be 192.168.90.1/24
On the network there are already some devices in this ip range some of them have dynamically assigned IP, some use the feature Make Static (which basically let device get ip from router, but on that specific MAC, router will lock specific ip, so technically no other device should get that IP if MAC is not the same) and lastly some of the devices got dynamic IP assigned and later they were (e.g. in windows settings) switched to static IP (uplug cable and plug back, computer will get static IP)
If there will be another device with the same IP, it will not work from the boot of device.
We noticed that when we use dietpi-launcher to change eth0 status from dhcp to static or vice versa, it will not make change in /etc/network/interfaces.d/eth0 (it is always dhcp)