The only 'solution' I've seen to this is to create a new user account and install TT under that, which is not ideal but has worked for some people. Someone on a different thread thought there was some issue to do with keychain/passwords related to old versions, but couldn't nail it down (so it's not connectivity issue, but some other issue connecting to the mothership).
FWIW here's one of the threads on this - but mixes up Windows and Mac issues, and kicked off around the time there was an actual outage on the TT side one Friday afternoon but when that resolved a small number of folks were still stuck.
https://ttlc.intuit.com/community/taxes/discussion/re-why-can-t-i-get-turbotax-to-connect-to-the-int...
