first of all, DietPi is Raspberry OS in an extrem slim/diet version. Due to this DietPi is running with a reduced number of packages installed. Probably plain RPi OS by default has Avahi-Daemon installed. You could try and have it installed using dietpi-software.
DNS resolution is done by your router. Did you checked the name that is present on your router? You could try a revers lookup from your Windows box
nslookup <IP-address>