Yes - it is perfectly safe. The only caveat is that network manager cannot deduct whether you have an internet connection or not.
There is several methods to accomplish this
- change the righthand part to a trusted domain
or
- remove the righthand part of uri
- set interval to 0
I went with number 1
➜ ~ cat /etc/NetworkManager/conf.d/20-connectivity.conf
[connectivity]
uri=https://iso.uex.dk/check_network_status.txt
interval=300