Getting the following error on dietpi when i install new software.
First of all, there is no need to do screen prints. You could simply copy the error message from SSH terminal 
Your issue seems be network related as you are not able to connect to webmin package source. This could be temporarily. Maybe you could try again later on.
I did ping google.com and my net working so I’m wondering if it a webmin problem
I did a test and for me the repository is reachable
Hit:5 https://archive.raspberrypi.org/debian bullseye InRelease
Ign:6 https://download.webmin.com/download/repository sarge InRelease
Get:7 https://download.webmin.com/download/repository sarge Release [16.9 kB]
Get:8 https://download.webmin.com/download/repository sarge Release.gpg [173 B]
Get:9 https://download.webmin.com/download/repository sarge/contrib arm64 Packages [1379 B]
Fetched 18.4 kB in 4s (4694 B/s)
Reading package lists...
[ OK ] DietPi-Software | APT update
[ INFO ] DietPi-Software | APT install for: webmin, please wait...
Reading package lists...
URL download.webmin.com is resolving same as yours
root@DietPi:~# nslookup download.webmin.com
Server: 9.9.9.9
Address: 9.9.9.9#53
Non-authoritative answer:
Name: download.webmin.com
Address: 104.207.151.13