Here's a good place to start: https://helpx.adobe.com/flash-player/kb/removing-sandbox-restrictions-your-safari.html
I have a early 2015 model Mac running macOS Sierra with Safari as my browser.
]]>Connect can't be developed to be compatible with future changes of software from other manufactures. I'm sure that Adobe is working on a solution, but it will be in the form of an update to address the changes that Apple made.
For what it's worth, the Connect Add-in will launch with any other web browser.
I'm sorry to hear you have had frustration with Connect, but in this case your frustration would be more appropriately sent to Apple.
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