I know someone already responded to you, and I don't mean to pile on, but commonly used words like "Critical" should never be privately owned. Not now. Not ever.
“Critical Notes,” however, is close enough in domain and sound to “Critical Role” for legitimate questions to be raised. There is already a cottage industry of puns on the “Critical Role” name in the D&D fanbase. This would seem quite likely to be another one of them.
Again, this is not a legal analysis. This is a decency analysis.
I might be more simpathetic with their naming choice if it would have been an accidental thing. It could be that the makers of critical-notes never heard of the brand Critical Role, they just settled on the same word because of the game term. This is unlikely to be the case. Critical notes mention on their frontpage that they support the Exandrian calendar for note taking. Exandria, and thus the exandrian calendar, is the invention of Critical Role’s Dungeon Master. The chance that they heard about Exandria but haven’t heard about Critical Role is basically zero.