You don't need arc or optical output to finish setting up the streambar. Yes it will put screen saying you don't have hdmi-arc, click your tv doesn't have one, then when it ask if you optical and separate hdmi plugged in click yes and go on activating the streambar.
You need an arc or optical output if you want to hear other components connected to your tv through the streambar, but you don't need them if your only source is the roku built-in to the streambar. If you can live that, it should fine.
I have streambar connected to computer monitor, no arc or optical. It acts as the computer speakers, and I can stream apps and leave audio with streambar and video with monitor.
Edmund Roku Community Streaming Expert
Help others find this answer and click "Accept as Solution." If you appreciate my answer, maybe give me a Kudo.