As @francisp mentions, this looks like a DNS issue.
However:
This is adjusting the DNS server on Supervisor level (used by Home Assistant Core, Add-ons etc.).
The problem is on the OS side. When your router is not providing a default DNS server, the OS should fall back to 1.1.1.1 automatically. But maybe this DNS server is blocked by your router/ISP/country. To double check if 1.1.1.1 is indeed not available, you can explicitly set this DNS server using (replace x with a IP which is not assigned by your routers DHCP range):
ha network update end0 --ipv4-method static --ipv4-address 192.168.41.x/24 --ipv4-nameserver 1.1.1.1
Alternatively, try a different DNS server, e.g. the Google DNS server:
ha network update end0 --ipv4-method static --ipv4-address 192.168.41.x/24 --ipv4-nameserver 8.8.8.8
You can use ha supervisor restart to make the Supervisor start again and try to fetch Home Assistant Core.