Luckily for me I've never experienced your problem, but ...
When the setup fails to complete after the software update runs, here are a couple of things that some people have found to work for them. They may not be universally successful, but they are worth a try.
Easiest to try, so try this first: Restart your router, even if other devices have no trouble connecting. When your router has completed its startup, try repeating your Roku setup.
More involved: Repeat the setup by connecting to a different wifi network - perhaps via a wifi hotspot on your mobile phone or by taking it to a friend's house - and see if it will complete the startup. If successful, then redo the wifi connection to use your intended wifi network via Settings > Network > Set up connection.
Roku Community Streaming Expert
I am not a Roku employee, only a user like you. Please, no support questions via private message -- post them publicly to the Community where others may benefit as well.
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