One of my sites met this issue for a couple of months already. I have tried to uninstall / re-install this JetPack plug-in many times, but could not fix it until saw this article. For me, the solution 2 - Install Really Simple SSL works.
After installed and activate plug-in - Really Simple SSL, you will have to activate SSL for your site in the plug-in.
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https://www.urtech.ca/2019/06/solved-wordpress-jetpack-error-updating-settings-fetchnetworkerror/

We run more than a dozen sites with nearly all of the configured the same way but one of our sites kept erroring out with “WordPress JetPack Error Updating Settings – FetchNetworkError” when we were trying to change settings in JetPack.
We suspect this error is related to our use of SSL via the CloudFlare CDN (Content Delivery Network) but were not able to prove it,