DNS Settings are not getting saved

10.14.* is Mojave, not High Sierra.

Try doing the same thing in Safe Mode. Do the settings stick?

If they do, then probably something that is running when you boot normally and log in to your account may be interfering.

In that case, please run Etrecheck and post its report here.

If the setting does not stick even in Safe Mode then you may want to delete the Wifi network service by pressing “-“ on the bottom left and then add it again.

After making the changes you "apply" on the bottom of the window where you make the changes, then you get to the opening window and you have to apply also there at the bottom !

1..

Hosts file corrupt. The file is in /private/etc/hosts. Open it in Textedit or BBedit, replace all that is in there with, exactly:

##

# Host Database

#

# localhost is used to configure the loopback interface

# when the system is booting. Do not change this entry.

##

127.0.0.1 localhost

255.255.255.255 broadcasthost

::1 localhost

2.. Then remove AdobeResourceSynchronizer.app from the LoginItems: it is only for Adobe's pleasure there. Does not have to run continuously.

3.. Do not run more than one VPN, you have three or more!, uninstall the ones that you do not want, leave one.

4.. It may be that Valvesoftware-steamclean is not yet compatible with Mojave: check tha on he developers website or in https://roaringapps.com

5.. Check Capture One compatibilty too to be sure.

6.. Battery should be at max CycleCount: 1000 cycles, condition: Normal

your cycle count indicates that you must keep an eye on it.

7.. Shutdown the mac

do a PRAM reset: Reset NVRAM or PRAM on your Mac - Apple Supporthttps://support.apple.com/en-us/HT204063

8.. Restart the mac