The banner which prompts you for notification requests on the Roblox website no longer has a way to quickly dismiss it. This is a regression, as previously there was a small cross you could click to have the prompt disappear.
Unfortunately I cannot provide a definitive list of steps to follow. I believe on a new sign-in (no existing cookies/browser cache) you will be prompted.
I was able to test this on Google Chrome Version 77.0.3865.90 (Official Build) (64-bit).
As a temporary workaround, I tried allowing notifications. This got rid of the banner, however when I went into site settings and blocked notifications again the banner re-appeared after refreshing the page.