TL,DR: Safesearch was enabled on my router's parental controls and was overridng my Google account settings.
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After trying several suggestions in other posts, I was at a dead end when nothing worked.
My problem was that I would get a restricted content error while trying to play a video on the YouTube channel on my Roku TV while logged into my Google account.
My account was configured with my age, so that solution did not apply.
As I looked through my Google account settings using my phone, I found that safesearch was "locked on." It told me that my network was responsible for the current configuration.
On my phone, I turned off Wi-Fi, and voila, the safesearch setting could now be toggled off.
My Roku TV , however, only works using the local network. Realizing that the problem was a local network configuration, I was able to log into my router and adjust it's parental controls for safe browsing.
My router had a specific setting for YouTube restriction that was set to high (options being high, moderate or off).
Understand this: In order to get my Roku TV to play restricted content on the YouTube channel I had to turn off a safe browsing parental control on my router
The upside is that my router's parental controls we're being enforced even inside the YouTube channel of my Roku TV, and the downside was that my Google account settings were not ultimately authoritative.
Personally, I see this as a win for security policy (safe browsing).
Depending on perception, there are pros and cons to how this appears to be working today.
I hope this solution works for others.
Have a great day!
